Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands		9 Months Ended
	Dec. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Organization And Description Of Business [Line Items]
New Accounting Pronouncement Effect Of Adoption On Additional Paid In Capital	$ 2,458,889
New Accounting Pronouncement Effect Of Adoption On Retained Earnings	652,704
New Accounting Pronouncement Effect Of Adoption On Cash Flow Amortization Of Deferred Stock Compensation			$ 8,106
New Accounting Pronouncement Effect Of Adoption On Cash Flow Accrued Payroll And Employee Benefits			970
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Provided By Operating Activities			229,045
New Accounting Pronouncement Effect Of Adoption On Cash Flow Repurchase Of Common Stock For Employee Withholding Obligations			(9,264)
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Used In Financing Activities			(201,903)
Previously Reported Member
Organization And Description Of Business [Line Items]
New Accounting Pronouncement Effect Of Adoption On Additional Paid In Capital	2,458,735
New Accounting Pronouncement Effect Of Adoption On Retained Earnings	$ 652,858
New Accounting Pronouncement Effect Of Adoption On Cash Flow Amortization Of Deferred Stock Compensation			5,505
New Accounting Pronouncement Effect Of Adoption On Cash Flow Accrued Payroll And Employee Benefits			(5,693)
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Provided By Operating Activities			219,781
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Used In Financing Activities			$ (192,639)
Accounting Standards Update 2016-09 Member
Organization And Description Of Business [Line Items]
New Accounting Pronouncement Effect Of Adoption On Additional Paid In Capital		$ 154
New Accounting Pronouncement Effect Of Adoption On Retained Earnings		(154)
New Accounting Pronouncement Effect Of Adoption On Cash Flow Amortization Of Deferred Stock Compensation		2,601
New Accounting Pronouncement Effect Of Adoption On Cash Flow Accrued Payroll And Employee Benefits		6,663
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Provided By Operating Activities		9,264
New Accounting Pronouncement Effect Of Adoption On Cash Flow Repurchase Of Common Stock For Employee Withholding Obligations		(9,264)
New Accounting Pronouncement Effect Of Adoption On Cash Flow Net Cash Used In Financing Activities		$ (9,264)