Revenue - Impact of Adoption on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Revenue	$ 107,944	$ 95,630	$ 96,080	$ 87,635	$ 97,963	$ 82,256	$ 78,016	$ 68,439	$ 387,289	$ 326,674	$ 228,504
Cost of revenue									113,965	$ 98,981	$ 75,433
Balance Without ASC 606 Adoption [Member] | ASC 606 [Member]
Disaggregation Of Revenue [Line Items]
Revenue									386,212
Cost of revenue									113,441
Adjustments Due to ASC 606 [Member] | ASC 606 [Member]
Disaggregation Of Revenue [Line Items]
Revenue									1,077
Cost of revenue									$ 524