Shareholders' Equity - Reconciliation of Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Shareholders’ Equity:
Beginning balance			$ 85,580
Net loss	$ (3,438)	$ 28,927	(15,674)	$ 54,837
Other comprehensive income	(404)	$ 711	(393)	$ 885
Exercise of stock options			535
Stock-based compensation expense			4,358
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	$ 78,546		$ 78,546