Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 11,237	$ (15,128)	$ (19,111)
Change in unrealized loss on investments	53	(258)	(86)
Change in minimum postretirement medical obligation	527	318	(1,066)
Change in unrealized loss on hedge contracts	0	0	(40)
Other comprehensive income (loss)	580	60	(1,192)
Total comprehensive income (loss)	$ 11,817	$ (15,068)	$ (20,303)