Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 18,350	$ 15,109
Income tax benefit	(3,740)	(3,141)
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	4,519	3,701
Selling and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	7,374	4,658
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	4,560	3,637
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation before tax	$ 1,897	$ 3,113