Revenue from Contracts with Customers - Cumulative Effect of Changes to Company's Condensed Consolidated Balance Sheet from Modified Retrospective Adoption of Asc 606 (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 8,123		$ 8,852
Accumulated deficit	(315,630)		$ (305,056)
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net		$ 8,987
Accumulated deficit		(304,921)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	325	135
Accumulated deficit	$ 325	$ 135