Summary of Significant Accounting Policies - Summary of Reflection of New Adopted Standards in Selected Consolidated Statement of Cash Flow (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net income	$ 35,722	$ 20,016	$ 76,882	$ 53,710
Stock-based compensation expense			26,921	16,306
Deferred income taxes, net			10,234	2,913
Deferred contract costs			$ (27,487)	(22,330)
Net cash provided by operating activities				55,293
As Previously Reported [Member]
Cash flows from operating activities
Net income		14,221		39,835
Stock-based compensation expense				17,524
Deferred income taxes, net				(6,760)
Net cash provided by operating activities				55,293
Adjustments [Member]
Cash flows from operating activities
Net income		$ 5,795		13,875
Stock-based compensation expense				(1,218)
Deferred income taxes, net				9,673
Deferred contract costs				$ (22,330)