Quarterly report pursuant to Section 13 or 15(d)

Notes Receivable from Partners - Additional Information (Detail)

v3.10.0.1
Notes Receivable from Partners - Additional Information (Detail) - Partners - USD ($)
9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Dec. 31, 2016
Aug. 31, 2009
Jan. 31, 2008
Related Party Transaction [Line Items]          
Term of promissory notes receivable in the form of five or six year interest-bearing promissory notes and/or in the form of nine year interest-bearing limited recourse promissory notes        
Notes receivable from partners $ 921,000 $ 1,918,000 $ 2,085,000    
Allowance for credit losses on notes receivable 0 0      
Limited Recourse          
Related Party Transaction [Line Items]          
Interest rates of promissory notes       2.77% 3.53%
Notes receivable from partners 0 825,000      
Full Recourse          
Related Party Transaction [Line Items]          
Notes receivable from partners $ 921,000 $ 1,093,000