Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 45,174	$ 33,562	$ 30,173
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Benefit plan liability adjustments - net gain (loss) (net of tax of $(36), $189 and $(73), respectively)	68	(351)	139
Reclassification adjustment of benefit plan liability - net gain (loss) (net of tax of $(33), $(16) and $(23), respectively)	61	29	43
Reclassification adjustment of cash flow hedges settled and included in net income (loss) (net of tax of $319, $(364) and $(23), respectively)	383	(300)	41
Other comprehensive income (loss), net of tax	512	(622)	223
Comprehensive income (loss), net of tax	$ 45,686	$ 32,940	$ 30,396