Debt (Summary of Senior Notes) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Debt Instrument [Line Items]      
Senior note carrying value $ 2,568,546   $ 1,576,082
Debt Issuance Costs, Net [1] (19,699)   (12,163)
Estimated fair value $ 2,663,408   $ 1,643,651
Unsecured Senior Notes 5.25% due June 2015      
Debt Instrument [Line Items]      
Stated interest rate 5.25%   5.25%
Debt Instrument, Maturity Date, Description June 2015   June 2015
Unsecured Senior Notes 6.50% due May 2016      
Debt Instrument [Line Items]      
Stated interest rate 6.50%   6.50%
Senior note carrying value [2] $ 465,245   $ 465,245
Debt Instrument, Maturity Date, Description May 2016   May 2016
Unsecured Senior Notes 7.625% due October 2017      
Debt Instrument [Line Items]      
Stated interest rate 7.625%   7.625%
Senior note carrying value [3] $ 123,000   $ 123,000
Debt Instrument, Maturity Date, Description October 2017   October 2017
4.250% unsecured senior notes due March 2021 [Domain]      
Debt Instrument [Line Items]      
Stated interest rate 4.25%    
Senior note carrying value [2] $ 300,000    
Debt Instrument, Maturity Date, Description March 2021    
5.500% unsecured senior notes due March 2026 [Domain]      
Debt Instrument [Line Items]      
Stated interest rate 5.50%    
Senior note carrying value [2] $ 700,000    
Debt Instrument, Maturity Date, Description March 2026    
Unsecured Senior Notes 7.875% due June 2032      
Debt Instrument [Line Items]      
Stated interest rate 7.875%   7.875%
Senior note carrying value [2] $ 300,000   $ 300,000
Debt Instrument, Maturity Date, Description June 2032   June 2032
Unsecured Senior Notes 6.375% due May 2033      
Debt Instrument [Line Items]      
Stated interest rate 6.375%   6.375%
Senior note carrying value [2] $ 400,000   $ 400,000
Debt Instrument, Maturity Date, Description May 2033   May 2033
Unsecured Senior Notes 6.00% due February 2035      
Debt Instrument [Line Items]      
Stated interest rate 6.00%   6.00%
Senior note carrying value [2] $ 300,000   $ 300,000
Debt Instrument, Maturity Date, Description February 2035   February 2035
Financial Services | Repurchase Agreement      
Debt Instrument [Line Items]      
Line of Credit Facility, Description   February 2, 2015  
Accounting Standards Update 2015-03 [Member]      
Debt Instrument [Line Items]      
Debt Issuance Costs, Net     $ (10,300)
[1] The carrying value of senior notes reflects the impact of premiums, discounts, and issuance costs that are amortized to interest cost over the respective terms of the senior notes. As discussed in Note 1, we adopted ASU 2015-03 in January 2016. We applied the new guidance retrospectively to all prior periods presented in the financial statements to conform to the 2016 presentation. As a result, $10.3 million of debt issuance costs at December 31, 2015, were reclassified from other assets to a reduction in senior notes.
[2] Redeemable prior to maturity; guaranteed on a senior basis by certain wholly-owned subsidiaries.
[3] Not redeemable prior to maturity; guaranteed on a senior basis by certain wholly-owned subsidiaries.