Convertible Notes (Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Nov. 17, 2017
Interest expense related to notes
Amortization of debt issuance costs and discounts	$ 7,656	$ 7,243	$ 6,854
Convertible senior notes
Interest expense related to notes
Total interest expense on convertible notes	10,028	9,615	9,226
Convertible senior notes \| 1.375% convertible notes due 2023
Interest expense related to notes
Coupon interest	2,372	2,372	2,372
Amortization of debt issuance costs and discounts	$ 7,656	$ 7,243	$ 6,854
Debt instrument, interest rate, stated percentage	1.375%	1.375%	1.375%	1.375%
Debt instrument, interest rate, effective percentage	4.90%	4.90%	4.90%

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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