Summary of Significant Accounting Policies - Summary of Adjustments to Quarterly Data Resulting from Adoption of New Standard in Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncement Early Adoption [Line Items]
Net cash provided from operating activities				$ 816,254	$ 387,068	$ 691,402
Net cash (used in) provided from financing activities				$ 322,937	$ (78,390)	(472,607)
Accounting Standards Update 2016-09
New Accounting Pronouncement Early Adoption [Line Items]
Net cash provided from operating activities	$ 90,785	$ 173,201	$ 205,837			691,402	$ 974,353	$ 757,373
Net cash (used in) provided from financing activities	(75,834)	(99,008)	(39,029)			(472,607)	271,203	226,159
As Reported | Accounting Standards Update 2016-09
New Accounting Pronouncement Early Adoption [Line Items]
Net cash provided from operating activities	87,424	169,604	202,037			683,700	954,135	743,538
Net cash (used in) provided from financing activities	$ (72,473)	$ (95,411)	$ (35,229)			$ (464,905)	$ 291,421	$ 239,994