Debt (Details) $ / shares in Units, shares in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2021 USD ($) $ / shares	Apr. 30, 2020 USD ($) D	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)
Debt Instrument [Line Items]
Proceeds from Convertible Note, net of issuance costs						$ 278,316,000
Common Stock, Par or Stated Value Per Share | $ / shares			$ 0.0001		$ 0.0001		$ 0.0001
Common stock, shares issued | shares			94,538		94,538		86,223
Accrued Interest			$ 2,695,000		$ 2,695,000		$ 1,078,000
Amortization of debt discount and issuance cost					917,000	149,000
Interest expense			2,078,000	$ 4,270,000	6,226,000	10,772,000
Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 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			$ 1,925,000		$ 5,769,000
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.0001
Debt instrument, term					7 years
Effective interest rate (as a percent)			2.72%		2.72%
Principal amount per convertible note		$ 1,000
Number of threshold consecutive trading days | D		30
Threshold business days | D		5
Conversion price (in dollars per share) | $ / shares	$ 38.79
Initial conversion rate	25.7785
Convertible to shares of common stock	7,411,704
Percentage of principal amount converted	100.00%
Carrying value			$ 280,085,000		$ 280,085,000
Convertible Notes | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Carrying value							$ 279,167,000
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%
Level 2
Debt Instrument [Line Items]
Fair value of liability			863,300,000		863,300,000
Line Of Credit-UBS
Debt Instrument [Line Items]
Maximum borrowing capacity								$ 50,000,000.0
Outstanding balance			$ 50,000,000.0		50,000,000.0
Interest expense				$ 200,000	$ 500,000	$ 700,000
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]
Debt, repayment amount		$ 79,200,000