Long-Term Debt - Components of Interest Expense Related to Convertible Notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total interest expense related to Convertible Notes	$ 133,800	$ 70,200	$ 63,500
3.25% Convertible Notes | Convertible Debt
Debt Instrument [Line Items]
Cash interest expense (coupon interest expense)	13,080	13,081	13,081
Non-cash amortization of discount on Convertible Notes	9,717	9,171	8,655
Amortization of debt issuance costs	1,749	1,600	1,462
Total interest expense related to Convertible Notes	24,546	23,852	$ 23,198
1.75% Convertible Notes | Convertible Debt
Debt Instrument [Line Items]
Cash interest expense (coupon interest expense)	9,653	1,174
Non-cash amortization of discount on Convertible Notes	14,563	1,718
Amortization of debt issuance costs	1,098	122
Total interest expense related to Convertible Notes	$ 25,314	$ 3,014