Quarterly report pursuant to Section 13 or 15(d)

Senior, Convertible Senior Notes (Details Textual)

v2.4.0.8
Senior, Convertible Senior Notes (Details Textual) (USD $)
Mar. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 200,000,000 $ 200,000,000
Line of credit facility, amount outstanding 0 0
Letters of Credit Outstanding, Amount 35,598,000 42,068,000
Percentage of wholly owned subsidiary 100.00%  
4.50% senior notes due two thousand eighteen [Member]
   
Debt Instrument [Line Items]    
Debt instrument, stated rate 4.50% 4.50%
Year in which senior notes due 2018 2018
7.00% senior notes due 2022 [Member]
   
Debt Instrument [Line Items]    
Debt instrument, stated rate 7.00% 7.00%
Year in which senior notes due 2022 2022
7.15% senior notes due 2020 [Member]
   
Debt Instrument [Line Items]    
Debt instrument, stated rate 7.15% 7.15%
Year in which senior notes due 2020 2020
Debt Instrument, Unamortized Premium 3,413,000 3,555,000
1.875% convertible senior notes due 2032 [Member]
   
Debt Instrument [Line Items]    
Debt instrument, stated rate 1.875% 1.875%
Year in which senior notes due 2032 2032
Revolving Credit Facility [Member]
   
Debt Instrument [Line Items]    
Minimum net worth required for compliance 360,000,000  
Leverage ratio 60.00%  
Line of credit facility, amount outstanding 0 0
Line of Credit Facility, Remaining Borrowing Capacity $ 164,400,000  
Consolidated EBITDA [Member] | Revolving Credit Facility [Member]
   
Debt Instrument [Line Items]    
Interest coverage ratio 1.50  
Consolidated Interest Incurred [Member] | Revolving Credit Facility [Member]
   
Debt Instrument [Line Items]    
Interest coverage ratio 1.00