Shareholders' Deficit- Equity Table (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Balance	$ (246,296)	$ (221,955)	$ (120,752)	$ (161,270)	$ (131,864)	$ (109,021)	$ (120,752)	$ (109,021)
Issuance of common stock in direct offering, net of offering costs				93,675
Exercise of stock options and warrants			6,333
Exercise of stock options	608	1,135		2,200	66	2,712
At the market offering costs			(241)
Stock-based compensation expense	5,694	3,117	3,271	3,824	3,822	3,476
Equity component of 2026 Notes, net of issuance costs				61,628
Purchases of 2026 Capped Calls				(23,223)
Equity component of early extinguishment of 2023 Notes				(22,073)
Termination of the 2023 Capped Call contracts related to debt repurchased				8,387
Tax benefit related to issuance of 2026 Notes, net of extinguishment				(12,011)
Net loss	(22,703)	(28,593)	(35,090)	(38,463)	(33,294)	(29,031)	(86,386)	(100,788)
Balance	(262,697)	(246,296)	(221,955)	(87,326)	(161,270)	(131,864)	(262,697)	(87,326)
Cumulative effect adjustment
Class of Stock [Line Items]
Balance			(75,476)				(75,476)
Common Stock
Class of Stock [Line Items]
Balance	624	622	616	545	545	542	616	542
Issuance of common stock in direct offering, net of offering costs				69
Exercise of stock options and warrants			6
Exercise of stock options	1	2		2		3
Balance	625	624	622	616	545	545	625	616
Additional Paid-in Capital
Class of Stock [Line Items]
Balance	694,132	689,882	751,304	635,121	631,233	625,048	751,304	625,048
Issuance of common stock in direct offering, net of offering costs				93,606
Exercise of stock options and warrants			6,327
Exercise of stock options	607	1,133		2,198	66	2,709
At the market offering costs			(241)
Stock-based compensation expense	5,694	3,117	3,271	3,824	3,822	3,476
Equity component of 2026 Notes, net of issuance costs				61,628
Purchases of 2026 Capped Calls				(23,223)
Equity component of early extinguishment of 2023 Notes				(22,073)
Termination of the 2023 Capped Call contracts related to debt repurchased				8,387
Tax benefit related to issuance of 2026 Notes, net of extinguishment				(12,011)
Balance	700,433	694,132	689,882	747,457	635,121	631,233	700,433	747,457
Additional Paid-in Capital | Cumulative effect adjustment
Class of Stock [Line Items]
Balance			(70,779)				(70,779)
Accumulated Deficit
Class of Stock [Line Items]
Balance	(941,052)	(912,459)	(872,672)	(796,936)	(763,642)	(734,611)	(872,672)	(734,611)
Net loss	(22,703)	(28,593)	(35,090)	(38,463)	(33,294)	(29,031)
Balance	$ (963,755)	$ (941,052)	(912,459)	$ (835,399)	$ (796,936)	$ (763,642)	(963,755)	$ (835,399)
Accumulated Deficit | Cumulative effect adjustment
Class of Stock [Line Items]
Balance			$ (4,697)				$ (4,697)