Debt - Schedule of Debt (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Debt [Roll Forward]
Total debt, Beginning balance	$ 6,073,444
Debt Issuances, Net	2,474,387
Repayments, Extinguishment and Assumptions, Net	(2,467,754)
Accretion and Amortization	7,845
Total debt, Ending balance	6,087,922
Mortgage Notes Payable and Other Debt [Member]
Debt [Roll Forward]
Total debt, Beginning balance	2,082,692
Debt Issuances, Net	144
Repayments, Extinguishment and Assumptions, Net	(154,254)
Accretion and Amortization	(5,925)
Total debt, Ending balance	1,922,657
Mortgages [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	2,071,038
Net premiums (discount), Beginning balance	24,652
Deferred costs, Beginning balance	(12,998)
Debt Issuances	187
Debt Issuances, Deferred costs	(43)
Repayments, Extinguishment and Assumptions	(154,093)
Repayments, Extinguishment and Assumptions of Debt, Premium, Amount	(191)
Repayments, Extinguishment and Assumptions of Debt, Deferred Costs, Amount	30
Accretion and Amortization, (Premiums) Discount	(8,384)
Accretion and Amortization, Deferred costs	2,459
Outstanding balance, Ending balance	1,917,132
Net premiums (discount), Ending balance	16,077
Deferred costs, Ending balance	(10,552)
Corporate Bonds [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	2,850,000
Net premiums (discount), Beginning balance	(1,232)
Deferred costs, Beginning balance	(27,274)
Total debt, Beginning balance	2,821,494
Debt Issuances	550,000
Debt Issuances, Discount	(3,696)
Debt Issuances, Deferred costs	(4,825)
Debt Issuances, Net	541,479
Accretion and Amortization, (Premiums) Discount	813
Accretion and Amortization, Deferred costs	4,823
Accretion and Amortization	5,636
Outstanding balance, Ending balance	3,400,000
Net premiums (discount), Ending balance	(4,115)
Deferred costs, Ending balance	(27,276)
Total debt, Ending balance	3,368,609
Convertible Debt [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	1,000,000
Net premiums (discount), Beginning balance	(7,782)
Deferred costs, Beginning balance	(7,960)
Total debt, Beginning balance	984,258
Repayments, Extinguishment and Assumptions	(597,500)
Repayments, Extinguishment and Assumptions, Net	(597,500)
Accretion and Amortization, (Premiums) Discount	3,873
Accretion and Amortization, Deferred costs	4,252
Accretion and Amortization	8,125
Outstanding balance, Ending balance	402,500
Net premiums (discount), Ending balance	(3,909)
Deferred costs, Ending balance	(3,708)
Total debt, Ending balance	394,883
Credit Facility [Member]
Debt [Roll Forward]
Outstanding balance, Beginning balance	185,000
Deferred costs, Beginning balance	0
Total debt, Beginning balance	185,000
Debt Issuances	1,934,000
Debt Issuances, Deferred costs	(1,236)
Debt Issuances, Net	1,932,764
Repayments, Extinguishment and Assumptions	(1,716,000)
Repayments, Extinguishment and Assumptions, Net	(1,716,000)
Accretion and Amortization, Deferred costs	9
Accretion and Amortization	9
Outstanding balance, Ending balance	403,000
Deferred costs, Ending balance	(1,227)
Total debt, Ending balance	$ 401,773