Stock-Based Compensation Expense Included in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 13,489	$ 10,818	$ 39,929	$ 30,634
Income tax benefit	(4,129)	(3,227)	(12,231)	(8,917)
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	3,613	3,117	10,913	8,711
Selling and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	3,976	3,468	11,482	9,395
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	3,420	2,260	10,306	7,480
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 2,480	1,983	$ 7,228	4,706
Acquisition-related
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax		$ (10)		$ 342