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Level 4 Debt (Details) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Debt [Line Items]      
Unamortized premium on 6.375% senior notes $ 1,623,000 $ 0  
Long-term debt 301,613,000 275,000,000  
Interest paid 18,400,000 18,100,000 16,700,000
Original Senior Notes [Member]
      
Debt [Line Items]      
6.375% senior notes, book value 250,000,000 250,000,000  
Percentage of Senior Notes tendered and accepted for exchange 100.00%    
6.375% senior notes [Member]
      
Debt [Line Items]      
6.375% senior notes, book value 299,990,000 250,000,000  
Interest rate 6.375%    
Additional Senior Notes [Member]
      
Debt [Line Items]      
6.375% senior notes, book value $ 49,990,000    
Premium rate on 6.375% senior notes 103.50%    
Percentage of Senior Notes tendered and accepted for exchange 99.98%