Debt - Athyrium Credit Facility (Details) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 01, 2018 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) item $ / shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) item $ / shares shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) shares
Debt instruments
Warrant exercisable | shares				297,988		297,988
Debt issuance costs			$ 50		$ 50
Interest expense		$ 2,180	$ 432	$ 6,335	$ 1,214
Warrants 2018
Debt instruments
Exercise Price | $ / shares		$ 12.18		$ 12.18
Warrant exercisable | shares				184,660		184,660
Remaining warrant exercisable upon condition | shares				86,175		86,175
Athyrium Credit Facility
Debt instruments
Aggregate principal amount	$ 110,000	$ 75,000		$ 75,000		$ 75,000
Cumulative accretion of exit fee		$ 146		$ 146		32
Present value of prepayments if prepayment occurs prior to the second anniversary (as a percent)	105.00%
Prepayments if prepayment occurs on or after the second anniversary of the applicable date of issuance but prior to the third anniversary (as a percent)	3.00%
Prepayments if prepayment occurs on or after the third anniversary (as a percent)	2.00%
Prepayments if prepayment occurs after the fourth anniversary (as a percent)	0.00%
Additional interest rate upon an event of default accrued (as a percent)	3.00%
Total interest rate (as a percent)	12.875%
Number of features of embedded derivative | item				2
Number of derivatives | item		1		1
Financial covenant amount	$ 10,000
Restricted Cash and Cash Equivalents		$ 10,000		$ 10,000		10,000
Fees to service provider	3,000
Debt issuance costs	$ 3,000	$ 4,211		$ 4,211		$ 4,806
Effective interest rate		11.63%		11.63%
Interest expense		$ 2,100		$ 6,200
Amortization of debt discount		200		600
Contractual coupon interest		$ 1,900		$ 5,600
Athyrium Credit Facility | Warrants 2018
Debt instruments
Warrant to purchase shares of common stock | shares	270,835
Exercise Price | $ / shares	$ 12.18456
Warrant exercisable | shares	184,660
Remaining warrant exercisable upon condition | shares	86,175
Initial fair value of the Warrant	$ 1,900
Term Loan A
Debt instruments
Aggregate principal amount	$ 75,000
Interest rate (as a percent)	9.875%
Exit fee of the total principal payments (as a percent)	1.00%
Cumulative accretion of exit fee	$ 800
Term Loan B
Debt instruments
Aggregate principal amount	$ 35,000