Liabilities - Convertible Senior Notes (Details) - Convertible Notes - USD ($) $ in Thousands		3 Months Ended
	Jan. 10, 2017	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt
Principal amount	$ 345,000	$ 345,000		$ 345,000
Interest rate (as a percent)	2.70%	2.70%
Proceeds received, net of transaction fees	$ 335,800
Unamortized debt discount		$ (37,804)		(40,820)
Unamortized transaction costs		(3,808)		(4,112)
Net carrying value		303,388		$ 300,068
Cash Interest Expense
Coupon interest expense		2,329	$ 2,329
Non-Cash Interest Expense
Amortization of debt discount		3,016	2,799
Amortization of transaction costs		304	282
Total Interest Expense		$ 5,649	$ 5,410
Convertible Debt, Fair Value by Fair Value Hierarchy Level		us-gaap:FairValueInputsLevel2Member
Estimated fair value		$ 283,800