Revenue Recognition - Summary of Impact of Adoption on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
STATEMENT OF OPERATIONS
Revenue	$ 38,925	$ 27,312	$ 105,266	$ 75,177
Net loss	(8,450)	$ (4,231)	(37,710)	$ (13,870)
Accounting Standards Update 2014-09 | Balances Without Adoption of ASC 606
STATEMENT OF OPERATIONS
Revenue	38,925		105,266
Net loss	(8,885)		(38,390)
Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
STATEMENT OF OPERATIONS
Net loss	$ 435		$ 680