Unsecured Convertible Senior Notes - Interest expense recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
2023 Unsecured Convertible Senior Notes
Interest Expense, Debt [Abstract]
Contractual interest expense	$ 1,484	$ 1,484	$ 4,453	$ 4,453
Amortization of debt issuance costs	167	156	493	459
Total	1,651	1,640	4,946	4,912
2026 Unsecured Convertible Senior Notes
Interest Expense, Debt [Abstract]
Contractual interest expense	2,954	2,954	8,861	8,861
Amortization of debt issuance costs	294	277	869	797
Total	$ 3,248	$ 3,231	$ 9,730	$ 9,658