Summary of Significant Accounting Policies - Effect of Adoption of Standard on Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 30,281	$ 17,571	$ 51,406	$ 28,966
Changes in operating assets and liabilities, net			3,046	(6,298)
Net cash provided by operating activities				79,317
Net decrease in cash and cash equivalents			$ (3,531)	(1,140)
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | As Originally Reported
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income		17,603		28,990
Changes in operating assets and liabilities, net				(6,322)
Net cash provided by operating activities				79,317
Net decrease in cash and cash equivalents				(1,140)
Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers | Effect of Change
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income		$ (32)		(24)
Changes in operating assets and liabilities, net				$ 24