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	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Revenue, Major Customer [Line Items]
Net (loss) income	$ (32,840)	$ 19,593
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Amortization of deferred costs	2,311	0
Changes in operating assets and liabilities:
Deferred costs	(10,106)	0
Deferred revenue	18,958	5,132
Net cash provided by operating activities	36,328	$ 23,938
Adjustments [Member] | Topic 606 [Member]
Revenue, Major Customer [Line Items]
Net (loss) income	(11,991)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Amortization of deferred costs	(2,311)
Changes in operating assets and liabilities:
Deferred costs	10,106
Deferred revenue	4,196
Net cash provided by operating activities	0
Balances Without Adoption of Topic 606 [Member] | Topic 606 [Member]
Revenue, Major Customer [Line Items]
Net (loss) income	(44,831)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Amortization of deferred costs	0
Changes in operating assets and liabilities:
Deferred costs	0
Deferred revenue	23,154
Net cash provided by operating activities	$ 36,328