Fair Value Measures (Fair Value of Financial Instruments by Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	$ 8,848,503	$ 10,513,781
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	9,199,993	10,874,827
Level 3 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	40,002	42,106
Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for investment	48,330	42,645
Level 3 [Member] | Mortgage Notes Payable and Other Debt, Net [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	3,210,413	3,805,761
Level 3 [Member] | Mortgage Notes Payable and Other Debt, Net [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	3,476,992	3,931,029
Level 3 [Member] | Corporate Bonds, Net [Member] | Senior Unsecured Note [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	2,547,059	2,546,499
Level 3 [Member] | Corporate Bonds, Net [Member] | Senior Unsecured Note [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	2,588,214	2,709,845
Level 3 [Member] | Convertible Debt, Net [Member] | Convertible Senior Notes [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	981,031	977,521
Level 3 [Member] | Convertible Debt, Net [Member] | Convertible Senior Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	1,020,495	1,088,069
Level 3 [Member] | Credit Facility [Member] | Credit Facilities [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	2,110,000	3,184,000
Level 3 [Member] | Credit Facility [Member] | Credit Facilities [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities	$ 2,114,292	$ 3,145,884