Annual report pursuant to Section 13 and 15(d)

Investments and Fair Value Measurements - Category of Financial Instruments Not Held at Fair Value (Detail)

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Investments and Fair Value Measurements - Category of Financial Instruments Not Held at Fair Value (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Carrying Amount    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Financial Assets, Cash and cash equivalents $ 53,822 $ 37,517
Financial Assets, Investments 626 335
Carrying Amount | Level 2    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Financial liabilities, Notes Payable 740 2,486
Fair Value    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Financial Assets, Cash and cash equivalents 53,822 37,517
Financial Assets, Investments 626 335
Fair Value | Level 2    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Financial liabilities, Notes Payable $ 740 $ 2,486