Long-Term Debt (Details) (USD $)
1 Months Ended 6 Months Ended
Mar. 31, 2012
Jun. 30, 2012
Dec. 31, 2011
Jul. 26, 2011
Long-term debt        
Less unamortized discount   $ (4,098,000) $ (4,517,000)  
Subtotal   456,002,000 483,033,000  
Less current portion   (16,638,000) (4,900,000)  
Long-term debt, net of current portion   439,364,000 478,133,000  
Amended Credit Facility
       
Long-term debt        
Maximum borrowing capacity       120,000,000
Increase in effective borrowing rate (as a percent)   0.42%    
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   12,000,000    
Term Loans
       
Long-term debt        
Subtotal   460,100,000 487,550,000  
Maximum borrowing capacity       490,000,000
Original issue discount (as a percent)   1.00%    
Increase in effective borrowing rate (as a percent)   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    
Prepayment of principal amount $ 25,000,000      
Effective interest rate under the Term Loans (as a percent)   6.40%    
Term Loans | Requirement when consolidated leverage ratio is between 1.25 and 2.25
       
Long-term debt        
Percentage of mandatory prepayments of excess cash flow depending on consolidated leverage ratio   25.00%    
Term Loans | Minimum | Requirement when consolidated leverage ratio is between 1.25 and 2.25
       
Long-term debt        
Consolidated leverage ratio   1.25    
Term Loans | Maximum
       
Long-term debt        
Percentage of mandatory prepayments of excess cash flow depending on consolidated leverage ratio   50.00%    
Term Loans | Maximum | Requirement when consolidated leverage ratio is between 1.25 and 2.25
       
Long-term debt        
Consolidated leverage ratio   2.25