Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Jun. 30, 2015
Jan. 31, 2018
Jul. 31, 2017
Jan. 31, 2017
Sep. 30, 2016
Jan. 31, 2016
Dec. 31, 2015
Oct. 31, 2015
Jul. 31, 2015
Jun. 30, 2015
Mar. 31, 2014
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Commitments And Contingencies [Line Items]                            
Operating lease rent expense                       $ 4,369,000 $ 3,760,000 $ 3,766,000
Sub-lease income                       278,000 289,000 433,000
Assets acquired under capital leases                       301,000   50,000
Depreciation expense                       975,000 737,000 719,000
Capital Lease Assets                            
Commitments And Contingencies [Line Items]                            
Depreciation expense                       142,000 124,000 123,000
Additional Office Space                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net         $ 10,000           $ 5,000      
Refundable security deposit                     $ 3,000      
Lease commencement date         Oct. 01, 2017           May 01, 2014      
Lease expires         Nov. 30, 2024           Jul. 31, 2019      
Number of rent free periods                     3 months      
Rent credit         $ 40,000,000                  
Additional Office Space | Amendment Number Two                            
Commitments And Contingencies [Line Items]                            
Lease commencement date         Jan. 16, 2018                  
Lease expires         Nov. 30, 2028                  
Lease expansion date         Jan. 12, 2018                  
Office Space | Charlottesville, VA.                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net                   $ 2,000        
Refundable security deposit $ 2,000                 $ 2,000        
Lease commencement date                   Jun. 30, 2015        
Lease expires                   Jun. 30, 2018        
Number of rent free periods                   2 months        
Office Space | Bedminster, NJ.                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net                       $ 11,000    
Lease expires                       Mar. 31, 2022    
Number of rent free periods                       4 months    
Office Space | Princeton, NJ.                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net           $ 6,000           $ 5,000    
Lease commencement date           Apr. 23, 2016                
Lease expires           Aug. 31, 2022           Apr. 30, 2016    
Number of rent free periods           5 months                
Office Space | New York City                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net             $ 446,000              
Lease commencement date             Oct. 01, 2017              
Lease expires             Sep. 30, 2028              
Number of rent free periods             12 months              
Payments for tenant improvements             $ 2,080,000              
Office Space | Livingston, NJ                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net           $ 2,000                
Office Space | Boston, MA | Subsequent Event                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net   $ 33,000                        
Lease commencement date   Jan. 01, 2018                        
Lease expires   Apr. 30, 2023                        
Number of rent free periods   1 month                        
Office Equipment                            
Commitments And Contingencies [Line Items]                            
Capital lease obligation                       $ 299,000 267,000  
Office Equipment | Telephone System                            
Commitments And Contingencies [Line Items]                            
Lease expires                       Nov. 30, 2018    
Assets acquired under capital leases                       $ 321,000    
Capital lease, period                       5 years    
Capital lease, minimum monthly payment                       $ 5,000    
Office Equipment | Copier                            
Commitments And Contingencies [Line Items]                            
Lease expires       Dec. 31, 2018       Oct. 31, 2018 Jun. 30, 2018          
Assets acquired under capital leases       $ 11,000       $ 18,000 $ 21,000          
Capital lease, period       2 years       3 years 3 years          
Capital lease, minimum monthly payment       $ 1,000       $ 1,000 $ 1,000          
Office Equipment | Two Copiers                            
Commitments And Contingencies [Line Items]                            
Lease expires       Jan. 31, 2022                    
Assets acquired under capital leases       $ 152,000                    
Capital lease, period       5 years                    
Capital lease, minimum monthly payment       $ 3,000                    
Office Equipment | Four Copiers                            
Commitments And Contingencies [Line Items]                            
Lease expires     Jun. 30, 2020                      
Assets acquired under capital leases     $ 72,000                      
Capital lease, period     3 years                      
Capital lease, minimum monthly payment     $ 2,000                      
Office Equipment | Jamison                            
Commitments And Contingencies [Line Items]                            
Assets acquired under capital leases $ 253,000                          
Letter of Credit                            
Commitments And Contingencies [Line Items]                            
Refundable security deposit                       506,000 506,000  
Letter of Credit | Boston landlord                            
Commitments And Contingencies [Line Items]                            
Refundable security deposit                       80,000    
General and administrative                            
Commitments And Contingencies [Line Items]                            
Operating lease rent expense, net                       $ 4,091,000 $ 3,471,000 $ 3,333,000