Basis of Presentation and Summary of Significant Accounting Policies - Summary of Impacts of Adopting the New Standard on Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Major Customer [Line Items]
Net (loss) income	$ (9,781)	$ 23,083
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Amortization of deferred costs	1,041	0
Changes in operating assets and liabilities:
Deferred costs	(3,626)	0
Deferred revenue	700	(3,869)
Net cash provided by operating activities	22,502	$ 18,496
Adjustments [Member] | Topic 606 [Member]
Revenue, Major Customer [Line Items]
Net (loss) income	(3,629)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Amortization of deferred costs	(1,041)
Changes in operating assets and liabilities:
Deferred costs	3,626
Deferred revenue	1,044
Balances Without Adoption of Topic 606 [Member] | Topic 606 [Member]
Revenue, Major Customer [Line Items]
Net (loss) income	(13,410)
Changes in operating assets and liabilities:
Deferred revenue	1,744
Net cash provided by operating activities	$ 22,502