Liabilities - 2027 Convertible Senior Notes (Details)			6 Months Ended
	May 18, 2020 USD ($) D $ / shares	May 13, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt
Principal amount			$ 381,695,000	$ 345,000,000
Purchase of capped calls			10,313,000
Debt discount			59,589,000	$ 40,820,000
2027 Notes
Debt
Principal amount	$ 125,000,000.0		125,000,000
Interest rate (as a percent)	3.75%
Proceeds received, net of transaction fees	$ 121,900,000
Purchase of capped calls	$ 10,300,000
Conversion rate of the Notes to common stock, per $1,000 principal amount of Notes	0.0715372
Initial conversion price per share of common stock (in dollars per share) | $ / shares	$ 13.98
Multiples of principal holders may convert	$ 1,000
Threshold consecutive trading days for convertible debt | D	30
Stock price trigger (as a percent)	130.00%
Trading days | D	5
Number of consecutive business days	5 days
Maximum percentage of common stock conversion	98.00%
Measurement input	0.0910
Long-term Debt, Measurement Input	us-gaap:MeasurementInputDiscountRateMember
Debt discount	$ 34,200,000		$ 33,773,000
Transaction costs	3,100,000
Transaction costs allocated to the equity component	$ 800,000
2027 Notes | Capped Call Transactions
Debt
Aggregate price of capped call transaction		$ 10,300,000
Cap price of the capped call transactions (in dollars per share) | $ / shares		$ 18.46
2027 Notes | Minimum
Debt
Trading days | D	20