Comprehensive Income and Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Components of comprehensive income
Net income	$ 3,947	$ 7,062	$ 12,631	$ 17,671
Reclassification to interest expense	321	399	995	1,217
Deferred tax (expense) benefit	(59)	106	(193)	33
Mark-to-market of interest rate hedges	(158)	(689)	(464)	(1,307)
Comprehensive income	4,051	6,878	12,969	17,614
Accumulated other comprehensive loss
Mark-to-market of interest rate hedges, net of tax benefit	(1,881)		(1,881)		(2,219)
Minimum pension liability adjustments, net of tax benefit	(782)		(782)		(782)
Accumulated other comprehensive loss	$ (2,663)		$ (2,663)		$ (3,001)