Shareholders' Equity - Reconciliation of Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Shareholders’ Equity:
Beginning balance			$ 85,580
Net loss	$ (15,771)	$ 21,679	(31,445)	$ 76,516
Other comprehensive loss	8	$ (741)	(385)	$ 144
Exercise of stock options			535
Stock-based compensation expense			7,190
Employee share purchase plan share issuance			127
Share repurchases			(27,637)
Exercise of warrants (see Note 8)			2,911
Expiration of warrants (see Note 8)			2,167
Equity component of 2018 Notes (see Note 9)			26,699
Ending balance	$ 65,742		$ 65,742