Fair Value of Derivatives and Financial Instruments (Textual) (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Derivative
Credit Risk Related Contingent Features Termination Value	$ 0
Preferred Stock, Redemption Price Per Share	$ 50.00
Preferred Stock, Redemption Date	Oct. 01, 2026
Designated as Hedging Instrument | Interest Expense
Derivative
Change in fair value of interest rate derivatives included in AOCI and expected to be reclassified in the next 12 months	$ 2,900,000
Fixed Rate Debt
Derivative
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	3,500,000,000	$ 3,200,000,000
Notes Payable, Fair Value Disclosure	3,500,000,000	3,300,000,000
Floating Rate Debt [Member]
Derivative
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	1,000,000,000	1,300,000,000
Notes Payable, Fair Value Disclosure	$ 1,000,000,000	1,300,000,000
Minimum [Member] | Conventional Variable Rate Debt [Member]
Derivative
Debt Renewal Period	30 days
Maximum [Member] | Conventional Variable Rate Debt [Member]
Derivative
Debt Renewal Period	90 days
Fair Value, Measurements, Recurring [Member]
Derivative
Embedded Derivative, Fair Value of Embedded Derivative Asset	$ 21,300,000	21,200,000
Interest Rate Derivative Assets, at Fair Value	7,200,000	3,600,000
Interest Rate Derivative Liabilities, at Fair Value	$ 500,000	$ 1,300,000