Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Other Comprehensive Income (Loss), before Tax [Abstract]
Foreign currency translation adjustment	$ 86	$ 46	$ 135	$ (1)
Reclassification of net gains on derivative instruments to net income	(297)	(297)	(594)	(594)
Pension and postretirement medical liability adjustment	0	0	0	333
Other comprehensive loss	(211)	(251)	(459)	(262)
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0	0	0
Reclassification of net gains on derivative instruments to net income	114	106	228	220
Pension and postretirement medical liability adjustment	0	0	0	(128)
Other comprehensive loss	114	106	228	92
Other comprehensive (loss) income, net of tax:
Foreign currency translation	86	46	135	(1)
Reclassification of net gains on derivative instruments to net income	(183)	(191)	(366)	(374)
Pension and postretirement medical liability adjustment	0	0	0	205
Total Other Comprehensive Loss	(97)	(145)	(231)	(170)
Accumulated Other Comprehensive Income [Abstract]
Foreign currency translation	501		501		366
Derivative instruments designated as cash flow hedges	3,877		3,877		4,243
Pension and postretirement medical plans	(2,292)		(2,292)		(2,292)
Accumulated other comprehensive income	$ 2,086		$ 2,086		$ 2,317