Comprehensive Income and Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Components of comprehensive income
Net income	$ 4,060	$ 5,795	$ 8,684	$ 10,609
Reclassification to interest expense	335	404	674	818
Deferred tax (expense) benefit	(52)	90	(134)	(73)
Mark-to-market of interest rate hedge	(193)	(650)	(305)	(618)
Comprehensive income	4,150	5,639	8,919	10,736
Accumulated other comprehensive loss
Mark-to-market for interest rate hedges, net of tax benefit	(1,984)		(1,984)		(2,219)
Minimum pension liability adjustments, net of tax benefit	(782)		(782)		(782)
Accumulated other comprehensive loss	$ (2,766)		$ (2,766)		$ (3,001)