Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	0 Months Ended			3 Months Ended	0 Months Ended			3 Months Ended	0 Months Ended		3 Months Ended		0 Months Ended			0 Months Ended
	Mar. 31, 2012	Feb. 29, 2012 2012 Credit Agreement	Mar. 31, 2013 2012 Credit Agreement	Mar. 31, 2012 2012 Credit Agreement	Mar. 31, 2013 2012 Credit Agreement Eurodollar rate loans LIBOR	Feb. 29, 2012 2012 Credit Agreement Eurodollar rate loans LIBOR Minimum	Feb. 29, 2012 2012 Credit Agreement Eurodollar rate loans LIBOR Maximum	Feb. 29, 2012 2012 Credit Agreement Base rate loans and swingline notes Federal funds rate	Mar. 31, 2013 2012 Credit Agreement Base rate loans and swingline notes Base Rate	Feb. 29, 2012 2012 Credit Agreement Base rate loans and swingline notes Base Rate Minimum	Feb. 29, 2012 2012 Credit Agreement Base rate loans and swingline notes Base Rate Maximum	Mar. 31, 2013 Revolver	Feb. 29, 2012 Revolver	Feb. 29, 2012 Revolver Minimum	Feb. 29, 2012 Revolver Maximum	Feb. 29, 2012 Swingline Loans	Feb. 29, 2012 2008 Credit Facility
Long-term debt
Maximum borrowing capacity													$ 250,000			$ 10,000
Maximum borrowing capacity		350,000
Available balance												58,302
Description of variable rate					LIBOR	LIBOR	LIBOR	Federal funds rate	Base rate	Base rate	Base rate
Interest rate added to base rate (as a percent)					2.50%	1.75%	2.75%	0.50%	1.50%	0.75%	1.75%
Percentage of commitment fee on unused credit facility												0.35%		0.25%	0.50%
Current leverage ratio		3.75
Future leverage ratio		3.50
Consolidated cash flow coverage ratio		1.20
Deferred financing costs		1,497
Unamortized deferred financing costs written off	1,220																133
Outstanding credit facility												190,318
Outstanding letters of credit			$ 1,380
Average effective interest rate on borrowing including the effects of swaps (as a percent)			3.68%	4.00%