Long-Term Debt (Details) (USD $)	9 Months Ended			9 Months Ended		1 Months Ended	9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Amended Credit Facility	Sep. 30, 2011 Amended Credit Facility	Mar. 31, 2012 Term Loans	Sep. 30, 2012 Term Loans	Dec. 31, 2011 Term Loans	Jul. 26, 2011 Term Loans	Sep. 30, 2012 Term Loans Requirement when consolidated leverage ratio is between 1.25 and 2.25	Sep. 30, 2012 Term Loans Maximum	Sep. 30, 2012 Term Loans Maximum Requirement when consolidated leverage ratio is between 1.25 and 2.25	Sep. 30, 2012 Term Loans Minimum Requirement when consolidated leverage ratio is between 1.25 and 2.25	Sep. 30, 2012 Revolving Loans	Jul. 26, 2011 Revolving Loans
Long-term debt
Less unamortized discount		$ (3,892,000)	$ (4,517,000)
Subtotal		454,983,000	483,033,000				458,875,000	487,550,000
Less current portion		(7,300,000)	(4,900,000)
Long-term debt, net of current portion		447,683,000	478,133,000
Maximum borrowing capacity									490,000,000						120,000,000
Original issue discount (as a percent)							1.00%
Increase in effective borrowing rate (as a percent)				0.42%			0.18%
LIBOR							LIBOR
LIBOR plus interest rate (as a percent)							4.50%
Interest rate for term loan (as a percent)							5.75%
Quarterly principal payment							1,225,000
Annual principal payment							4,900,000
Percentage of mandatory prepayments of excess cash flow depending on consolidated leverage ratio										25.00%	50.00%
Prepayment of principal amount						25,000,000
Interest rate terms														bear interest at the alternative base rate or LIBOR, plus the applicable margin for each rate that fluctuates with the consolidated leverage ratio
Funds available under credit facility														116,600,000
Debt issuance costs	$ 12,019,000				$ 12,000,000
Effective interest rate under the Term Loans (as a percent)							6.40%
Consolidated leverage ratio												2.25	1.25