Debt (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended	12 Months Ended
	Apr. 29, 2019	Apr. 30, 2019	Aug. 31, 2017	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2019	Oct. 17, 2019	Apr. 26, 2019	Apr. 23, 2019	Jul. 31, 2018	Aug. 14, 2017	Aug. 08, 2017	Sep. 30, 2015
Debt Instrument [Line Items]
Issuance of common stock to Orbimed					$ 507
Common stock, shares issued		5,263,158			78,004,669	62,083,000		5,714,286	5,714,286	789,473	5,263,158	4,500,000
Stock issued (in dollars per share)		$ 19						$ 35	$ 35		$ 19	$ 20
Payment for debt issuance costs on long-term debt facility							$ 287
Amortization of debt discount					$ 457	$ 391	154
Interest expense					10,693	10,476	4,213
Net carrying amount					73,656	73,357
Line Of Credit-UBS
Debt Instrument [Line Items]
Maximum borrowing capacity															$ 50,000
Interest expense					1,700	1,600	1,000
Interest paid					1,700	1,500	500
Outstanding balance					50,100
Debt, interest accrued					$ 1,100
Line Of Credit-UBS | LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)					1.10%
Noncurrent assets
Debt Instrument [Line Items]
Amortization of debt discount					$ 200	100
Debt discount					900
2017 Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 100,000
Remaining borrowing capacity		$ 50,000	$ 50,000	$ 50,000		25,000								$ 25,000
Interest expense					9,000	8,600	$ 3,200
Interest paid					10,700	6,100
Repayments					$ 0
Additional interest in the event of default (as a percent)			3.00%
Issuance of common stock to Orbimed (in shares)	25,000
Debt instrument, term					84 months
Common stock, shares issued		25,000	300,000										300,000
Debt instrument, fee amount			$ 2,400											$ 300
Stock issued (in dollars per share)														$ 8.16
Debt discount			2,700
Debt, increase (decrease)			$ (2,000)
Debt principal balance					$ 75,000	75,000								$ 75,000
Less: unamortized debt discount					(1,344)	(1,643)
Net carrying amount					$ 73,656	$ 73,357
2017 Term Loan | Minimum
Debt Instrument [Line Items]
Remaining borrowing capacity		$ 25,000
Prepayment premium (as a percent)			2.50%
2017 Term Loan | Maximum
Debt Instrument [Line Items]
Prepayment premium (as a percent)			12.50%
2017 Term Loan | Base Rate
Debt Instrument [Line Items]
Spread on interest rate (as a percent)			8.75%
Base interest rate (as a percent)		8.25%	1.00%
Spread on base interest rate (as a percent)		1.00%
2017 Term Loan | LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)				8.75%
Base interest rate (as a percent)				1.00%
2017 Term Loan | LIBOR | Scenario of minimum borrowing capacity of drawn
Debt Instrument [Line Items]
Spread on interest rate (as a percent)		8.75%		8.25%
Base interest rate (as a percent)		1.00%		1.00%
2017 Term Loan | Noncurrent assets
Debt Instrument [Line Items]
Debt instrument, fee amount			$ 1,200