Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Components of comprehensive income
Net income	$ 2,629	$ 4,789	$ 4,626	$ 2,757	$ 3,792	$ 3,947	$ 4,060	$ 4,624	$ 14,800	$ 16,423	$ 22,186
Minimum pension liability adjustments									309	100	(234)
Reclassification to interest expense									1,141	1,320	1,587
Deferred income tax expense									(510)	(348)	(4)
Mark to market of interest rate hedges									(46)	(463)	(1,341)
Comprehensive income									15,694	17,032	22,194
Accumulated other comprehensive loss
Mark to market of interest rate hedges, net of tax benefit	(977)				(1,674)				(977)	(1,674)
Minimum pension liability adjustments, net of tax benefit	(521)				(718)				(521)	(718)
Accumulated other comprehensive loss	$ (1,498)				$ (2,392)				$ (1,498)	$ (2,392)