Liabilities - Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Non-Cash Interest Expense
Amortization of debt discount/transaction costs			$ 7,100	$ 6,778
Total Interest Expense	$ 6,806	$ 6,100	13,541	11,750
2023 Notes
Cash Interest Expense
Coupon interest expense	889	2,070	1,778	4,399
Non-Cash Interest Expense
Amortization of debt discount/transaction costs	$ 1,390	3,004	$ 2,754	6,325
Convertible Debt, Fair Value by Fair Value Hierarchy Level	Level 2		Level 2
Estimated fair value	$ 132,300		$ 132,300
2025 Notes
Cash Interest Expense
Coupon interest expense	1,159		2,319
Non-Cash Interest Expense
Amortization of debt discount/transaction costs	$ 1,185		$ 2,348
Convertible Debt, Fair Value by Fair Value Hierarchy Level	Level 2		Level 2
Estimated fair value	$ 158,800		$ 158,800
2027 Notes
Cash Interest Expense
Coupon interest expense	1,172	573	2,344	573
Non-Cash Interest Expense
Amortization of debt discount/transaction costs	$ 1,011	$ 453	$ 1,998	$ 453
Convertible Debt, Fair Value by Fair Value Hierarchy Level	Level 2		Level 2
Estimated fair value	$ 220,200		$ 220,200