Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Narrative) (Details)

v2.4.0.6
Long-Term Debt (Narrative) (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Apr. 08, 2012
Jun. 30, 2012
Dec. 31, 2011
Debt Instrument [Line Items]        
Senior Notes $ 227,143,000   $ 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%   5.07% 5.17%
Applicable margin interest on credit facility, low end     1.00%  
Applicable margin interest on credit facility, high end     1.875%  
Margin interest during period 1.00% 1.125%    
Decreases in marginal interest during period 0.50%   0.50%  
LIBOR rate 1.00%   1.00%  
Line of Credit Facility, Amount Outstanding 34,030,000   34,030,000 0
Line of Credit Facility, Interest Rate During Period 1.00% 1.125%    
Letter Of Credit [Member]
       
Debt Instrument [Line Items]        
Maximum borrowing capacity 150,000,000   150,000,000  
Line of Credit Facility, Amount Outstanding 52,600,000   52,600,000 49,900,000
Sweep Program [Member]
       
Debt Instrument [Line Items]        
Maximum borrowing capacity 20,000,000   20,000,000  
Five Year Senior Unsecured Revolving Credit Facility [Member]
       
Debt Instrument [Line Items]        
Maximum borrowing capacity 300,000,000   300,000,000  
Current borrowing capacity 200,000,000   200,000,000  
Minimum increments under the additional borrowings     $ 25,000,000