Liabilities - 2023 Convertible Senior Notes (Details) - USD ($) $ in Thousands			9 Months Ended
	May 18, 2020	Jan. 10, 2017	Sep. 30, 2020	Dec. 31, 2019
Debt
Principal amount			$ 381,695	$ 345,000
Proceeds from issuance of 2027 Notes, net of issuance costs			121,946
Repurchase of notes			81,240
Loss on extinguishment of debt			(3,046)
2023 Notes
Debt
Principal amount		$ 345,000	$ 256,695	$ 345,000
Interest rate (as a percent)		2.70%	2.70%
Proceeds from issuance of 2027 Notes, net of issuance costs		$ 335,800
Repurchased and retired amount	$ 88,300
Debt instrument carrying amount	78,100
Repurchase of notes	81,200
Loss on extinguishment of debt			$ 3,000
2027 Notes
Debt
Principal amount	$ 125,000		$ 125,000
Interest rate (as a percent)	3.75%
Proceeds from issuance of 2027 Notes, net of issuance costs	$ 121,900