Debt (Details)		1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) D	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 $ / shares shares	Apr. 30, 2019 shares	Aug. 31, 2017 USD ($) shares	Aug. 08, 2017 USD ($)	Sep. 30, 2015 USD ($)
Debt Instrument [Line Items]
Proceeds from Convertible Note, net of issuance costs					$ 278,316,000
Unamortized debt discount	$ 2,091,000		$ 2,091,000		$ 2,091,000
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.0001		$ 0.0001		$ 0.0001		$ 0.0001
Issuance of common stock to Orbimed (in shares) | shares					25,000
Issuance of common stock to Orbimed						$ 506,000
Common stock, shares issued | shares	85,281,000		85,281,000		85,281,000		78,005,000
Debt, repayment amount					$ 79,200,000
Payment of accrued interest					400,000
Accrued Interest	$ 2,965,000		$ 2,965,000		2,965,000
Amortization of debt discount and issuance cost				$ 336,000	149,000
Interest expense			4,270,000	2,672,000	10,772,000	8,117,000
Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount	287,500,000	$ 287,500,000	287,500,000		$ 287,500,000
Proceeds from Convertible Note, net of issuance costs		$ 278,300,000
Per annum interest rate (as a percent)		2.25%			2.25%
Interest expense			4,100,000		$ 7,479,000
Unamortized debt discount	$ 8,625,000		$ 8,625,000		$ 8,625,000
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.001		$ 0.001		$ 0.001
Debt instrument, term		7 years
Effective interest rate (as a percent)		8.27%
Principal amount per convertible note		$ 1,000
Number of threshold consecutive trading days | D		30
Threshold business days | D		5
Convertible, If-converted value in excess of principal	$ 173,000,000
Conversion price (in dollars per share) | $ / shares	$ 38.79		$ 38.79		$ 38.79
Initial conversion rate	25.7785
Convertible to shares of common stock	7,411,704
Percentage of principal amount converted	100.00%
Fair value of liability		$ 201,900,000
Carrying value	$ 199,959,000		$ 199,959,000		$ 199,959,000
Equity component	82,873,000	85,600,000	82,873,000		82,873,000
Debt Instrument, debt discount, Equity Component	81,400,000		81,400,000		81,400,000
Debt Instrument, debt discount, Liability Component	5,700,000		5,700,000		5,700,000
Debt issuance costs	558,000	$ 600,000	558,000		558,000
5 consecutive trading day period | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D		5
Percentage of conversion price		98.00%
20 trading days period | Convertible Notes
Debt Instrument [Line Items]
Threshold trading days | D		20
Percentage of conversion price		130.00%
Redeemable for cash on or after May 2024
Debt Instrument [Line Items]
Number of threshold consecutive trading days | D		20
Threshold trading days | D		30
Percentage of conversion price		130.00%
Percentage of principal amount converted		100.00%
Debt Component | Convertible Notes
Debt Instrument [Line Items]
Unamortized debt discount	6,057,000		6,057,000		6,057,000
Debt issuance costs	392,000		392,000		392,000
Measurement input, risk free interest rate | Convertible Notes
Debt Instrument [Line Items]
Debt Instrument, Measurement Input		7.832
Level 2 | Convertible Notes
Debt Instrument [Line Items]
Fair value of liability	201,900,000		201,900,000		201,900,000
Line Of Credit-UBS
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 50,000,000.0
Outstanding balance	49,000,000.0		49,000,000.0		49,000,000.0
Accrued interest	1,100,000		1,100,000		1,100,000
Interest expense			200,000	$ 400,000	$ 700,000	1,300,000
Line Of Credit-UBS | LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)					1.10%
2017 Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 100,000,000.0
Remaining borrowing capacity	50,000,000.0		50,000,000.0		$ 50,000,000.0				$ 50,000,000.0	$ 25,000,000.0
Outstanding balance										$ 75,000,000.0
Common stock, shares issued | shares								25,000	300,000
Debt, repayment amount		$ 79,200,000
Interest expense					2,500,000	$ 6,500,000
2017 Term Loan | Minimum
Debt Instrument [Line Items]
Remaining borrowing capacity	$ 25,000,000.0		$ 25,000,000.0		$ 25,000,000.0
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 | Minimum borrowing capacity drawn
Debt Instrument [Line Items]
Spread on interest rate (as a percent)					8.25%
Base interest rate (as a percent)					1.00%
2017 Term Loan | Noncurrent assets
Debt Instrument [Line Items]
Debt instrument, fee amount									$ 1,200,000