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Credit Facility and Other Long Term Debt - Components of Convertible Senior Notes (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	May 31, 2020	Sep. 30, 2016
Debt Instrument [Line Items]
Total principal payments due	$ 680,919	$ 1,100,000	$ 1,100,000
Total amount outstanding	662,903	1,003,556	997,347
Credit Facility borrowings	0	0	0
Non-current portion of long-term debt	662,903	1,003,556	997,347
Credit Facility
Debt Instrument [Line Items]
Total principal payments due	0	0	0
Unamortized debt issuance costs - Credit facility	(3,095)	(4,325)	(4,601)
1.50% Convertible Senior Notes
Debt Instrument [Line Items]
Unamortized debt issuance costs - Credit facility				$ (10,000)
1.50% Convertible Senior Notes \| Convertible Notes
Debt Instrument [Line Items]
Total principal payments due	80,919	500,000	500,000
Unamortized debt discount	(10,105)	(79,031)	(84,127)
Unamortized debt issuance costs - Credit facility	(1,086)	(8,763)	(9,403)
1.50% Convertible Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Unamortized debt issuance costs - Credit facility				$ (12,300)
3.25% Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Total principal payments due	600,000	600,000	600,000
Unamortized debt discount	(1,194)	(1,385)	(1,448)
Unamortized debt issuance costs - Credit facility	$ (2,536)	$ (2,940)	$ (3,074)		$ (5,400)