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Long-Term Debt - Summary of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Oct. 07, 2020	Dec. 31, 2019	Nov. 15, 2019	Jun. 10, 2014
Debt Instrument [Line Items]
Gross long-term debt	$ 1,703,324
Less: Unamortized discount	(112,798)		$ (139,981)
Deferred issuance costs	(11,505)		(14,058)
Total long-term debt	1,579,021		1,448,461
Less: Current portion	(396,801)		(385,532)
Total long-term debt, less current portion	1,182,220		1,062,929
Senior Notes \| 6.0% Senior Notes
Debt Instrument [Line Items]
Stated interest rate		6.00%
Gross long-term debt	0		650,000
Less: Unamortized discount			(8,425)
Deferred issuance costs			(1,466)
Total long-term debt			640,109
Senior Notes \| 4.625% Senior Notes
Debt Instrument [Line Items]
Stated interest rate		4.625%
Gross long-term debt	750,000		0
Less: Unamortized discount	(5,523)
Deferred issuance costs	(1,761)
Total long-term debt	742,716
Convertible Debt
Debt Instrument [Line Items]
Gross long-term debt	1,702,414		1,602,500
Convertible Debt \| 3.25% Convertible Notes
Debt Instrument [Line Items]
Stated interest rate					3.25%
Gross long-term debt	402,414		402,500
Less: Unamortized discount	(4,644)		(14,363)		$ (59,000)
Deferred issuance costs	(855)		(2,605)
Total long-term debt	396,915		385,532
Convertible Debt \| 1.75% Convertible Notes
Debt Instrument [Line Items]
Stated interest rate				1.75%
Gross long-term debt	550,000		550,000
Less: Unamortized discount	(102,631)		(117,193)	$ (118,900)
Deferred issuance costs	(8,889)		(9,987)	$ (2,800)
Total long-term debt	438,480		422,820
Loans Payable \| Paycheck Protection Program, CARES Act
Debt Instrument [Line Items]
Gross long-term debt	$ 910		$ 0