Summary of Significant Accounting Policies - Effect of Adoption of Standard on Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 21,125	$ 11,395
Changes in operating assets and liabilities, net	(12,261)	(12,765)
Net cash provided by operating activities	35,502	24,128
Net decrease in cash and cash equivalents	$ (4,224)	(828)
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		11,387
Changes in operating assets and liabilities, net		(12,757)
Net cash provided by operating activities		24,128
Net decrease in cash and cash equivalents		(828)
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		8
Changes in operating assets and liabilities, net		$ (8)