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 $)
6 Months Ended 12 Months Ended 6 Months Ended 12 Months Ended 6 Months Ended 12 Months Ended 6 Months Ended 12 Months Ended 6 Months Ended
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Jun. 30, 2014
4.50% senior notes due two thousand eighteen [Member]
Dec. 31, 2013
4.50% senior notes due two thousand eighteen [Member]
Jun. 30, 2014
7.00% senior notes due 2022 [Member]
Dec. 31, 2013
7.00% senior notes due 2022 [Member]
Jun. 30, 2014
7.15% senior notes due 2020 [Member]
Dec. 31, 2013
7.15% senior notes due 2020 [Member]
Jun. 30, 2014
1.875% convertible senior notes due 2032 [Member]
Dec. 31, 2013
1.875% convertible senior notes due 2032 [Member]
Dec. 31, 2012
1.875% convertible senior notes due 2032 [Member]
Jun. 30, 2014
Revolving Credit Facility [Member]
Dec. 31, 2013
Revolving Credit Facility [Member]
Jun. 30, 2014
Credit Facility Accordion Feature [Member]
Jun. 30, 2014
Consolidated EBITDA [Member]
Revolving Credit Facility [Member]
Jun. 30, 2014
Consolidated Interest Incurred [Member]
Revolving Credit Facility [Member]
Debt Instrument [Line Items]                                  
Line of credit facility, maximum borrowing capacity $ 400,000,000 $ 200,000,000                         $ 100,000,000    
Debt Instrument Maturity Year                         2018        
Available For Issuance                         200,000,000        
Minimum net worth required for compliance                         670,300,000        
Leverage ratio                         60.00%        
Interest coverage ratio                               1.50 1.00
Line of credit facility, amount outstanding 0   0                   0 0      
Letters of Credit Outstanding, Amount 26,743,000   42,068,000                            
Line of Credit Facility, Remaining Borrowing Capacity                         373,300,000        
Debt instrument, stated rate       4.50% 4.50% 7.00% 7.00% 7.15% 7.15% 1.875% 1.875%            
Percentage of wholly owned subsidiary 100.00%                                
Year in which senior notes due       2018 2018 2022 2022 2020 2020 2032 2032            
Aggregate principal amount of offering                   1,000              
Debt Instrument, Unamortized Premium               $ 3,271,000 $ 3,555,000                
Debt Instrument, Convertible, Conversion Ratio                   17.1985              
Debt Instrument, Convertible, Conversion Price                       $ 58.14