Long-term Debt - Interest expense recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Long-term Debt
Interest on convertible notes	$ 2,811	$ 2,734	$ 5,994	$ 5,469
Amortization of debt issuance costs	637	679	1,423	1,324
Debt issuance cost derecognized related to convertible debt transactions	789		4,344
Interest on finance lease	208	179	423	363
Interest on borrowings under financing agreement	2,264	199	4,055	199
Other interest	30	26	61	52
Total interest expense	$ 6,739	$ 3,817	$ 16,300	$ 7,407