Summary of Significant Accounting Policies - Summary of Reflection of New Adopted Standards in Selected Consolidated Balance Sheet Line Items (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Deferred contract costs	$ 28,920	$ 26,403
Long-term deferred contract costs	188,580	171,865
Liabilities and Stockholders' Equity
Deferred income tax liabilities, net		49,129
Additional paid-in capital	189,302	161,809
Retained earnings	$ 299,685	258,525
As Previously Reported [Member]
Assets
Deferred income tax assets, net		3,294
Liabilities and Stockholders' Equity
Additional paid-in capital		137,234
Retained earnings		137,255
Adjustments [Member]
Assets
Deferred contract costs		26,403
Deferred income tax assets, net		(3,294)
Long-term deferred contract costs		171,865
Liabilities and Stockholders' Equity
Deferred income tax liabilities, net		49,129
Additional paid-in capital		24,575
Retained earnings		$ 121,270