Notes Payable - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Interest expense recognized related to the Notes
Amortization of debt discount and issuance costs			$ 5,081	$ 12,356
Total interest expense	$ 9,670		12,073
Senior Notes 3.625 Percent Due 2029
Interest expense recognized related to the Notes
Contractual interest expense	4,531		5,651
Amortization of debt discount	168		217
Total interest expense	4,699		5,868
Senior Notes 3.875 Percent Due 2031
Interest expense recognized related to the Notes
Contractual interest expense	4,844		6,041
Amortization of debt discount	127		164
Total interest expense	4,971		6,205
Convertible senior notes due 2023
Interest expense recognized related to the Notes
Contractual interest expense	106	$ 344	276	688
Amortization of debt discount and issuance costs	69	484	328	968
Amortization of debt discount	1,287	5,694	4,315	11,388
Total interest expense	$ 1,462	$ 6,522	$ 4,919	$ 13,044