Financial Instruments - Carrying Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 29,655	$ 33,153
Accounts receivable, net	10,446	10,347
Accounts payable	2,272	2,614
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	29,655	33,153
Accounts receivable, net	10,446	10,347
Accounts payable	$ 2,272	$ 2,614