Summary of Significant Accounting Policies -Summary of Cumulative Effect of Changes Made to the Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 4,969		$ 4,005
Deferred tax asset / (liability)	505		126
Equity:
Accumulated deficit	(59,321)		$ (57,664)
Accounting Standards Update 2014-09
Assets
Accounts receivable		$ 4,332
Deferred tax asset / (liability)		52
Equity:
Accumulated deficit		(57,411)
Accounting Standards Update 2014-09 | Adjustments due to ASC 606
Assets
Accounts receivable	(150)	327
Deferred tax asset / (liability)	74	(74)
Equity:
Accumulated deficit	$ (76)	$ 253