Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Narrative) (Details)

v2.4.0.6
Long-Term Debt (Narrative) (Details) (USD $)
9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Debt Instrument [Line Items]    
Senior Notes $ 227,143,000 $ 262,857,000
Periodic principal payments 35,700,000  
Fixed interest rate, minimum 4.00%  
Fixed interest rate, maximum 5.85%  
Effective average interest rate 5.07% 5.17%
Applicable margin interest on credit facility, low end 1.00%  
Applicable margin interest on credit facility, high end 1.875%  
LIBOR rate 1.00%  
Line of Credit Facility, Amount Outstanding 49,380,000 0
Applicable Margin Percentage, Interest Rate During Period 1.125%  
Applicable Margin Percentage, Interest Rate at Period End 0.50%  
Letter Of Credit [Member]
   
Debt Instrument [Line Items]    
Maximum borrowing capacity 150,000,000  
Line of Credit Facility, Amount Outstanding 52,600,000 49,900,000
Sweep Program [Member]
   
Debt Instrument [Line Items]    
Maximum borrowing capacity 20,000,000  
Five Year Senior Unsecured Revolving Credit Facility [Member]
   
Debt Instrument [Line Items]    
Maximum borrowing capacity 300,000,000  
Current borrowing capacity 200,000,000  
Minimum increments under the additional borrowings $ 25,000,000  
Maximum [Member]
   
Debt Instrument [Line Items]    
Applicable Margin Percentage, Interest Rate During Period 1.125%  
Minimum [Member]
   
Debt Instrument [Line Items]    
Applicable Margin Percentage, Interest Rate During Period 1.00%