Shareholders' Equity - Reconciliation of Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Shareholders’ Equity:
Beginning balance	$ 85,580
Net loss	(12,236)	$ 25,910
Other comprehensive income	11	$ 174
Stock-based compensation expense	2,134
Share repurchases	(20,212)
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	$ 87,054