Notes Payable - Convertible Note Hedge and Warrant Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
	Apr. 15, 2019	Jun. 30, 2015	Mar. 31, 2020	Dec. 31, 2019
Notes Payable
Long-term asset			$ 15,847	$ 31,366
Long-term liability			$ 12,207	$ 24,260
Net derivative issuance cost		$ 21,100
Convertible Note Hedge
Notes Payable
Shares issuable upon conversion of debt (in shares)			20,249,665
Conversion price (in dollars per share)	$ 14.51		$ 16.58
Long-term asset		91,900
Note Hedge Warrant Derivatives
Notes Payable
Shares into which warrants may be converted (in shares)			20,249,665
Trading day period			150 days
Long-term liability		$ 70,800
Note Hedge Warrants
Notes Payable
Warrants strike price (in dollars per share)	$ 18.82		$ 21.50
Note Hedge Warrants | 2.25% Convertible Senior Notes due 2022
Notes Payable
Shares issuable upon conversion of debt (in shares)	23,135,435