Notes Payable and Revolving Lines of Credit - Schedule of Components of Notes Payable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Variable Rate Interest
Notes payable to Trusts	$ 3,240,938
Notes payable, net	3,213,588	$ 2,758,567
Notes Payable [Member]
Fixed Rate Interest
Notes payable at fixed rate of interest	2,297,968	1,613,490
Variable Rate Interest
Notes payable at variable rate of interest	642,970	1,094,985
Notes payable to Trusts	3,240,938	2,782,300
Plus: Premium on notes payable	0	872
Unamortized debt issuance costs	(27,350)	(24,605)
Notes payable, net	$ 3,213,588	$ 2,758,567
Fixed rate debt due date, start	2017-03	2016-03
Fixed rate debt due date, end	2026-09	2023-02
Variable rate debt due date, start	2017-01	2016-07
Variable rate debt due date, end	2023-10	2021-03
Notes Payable [Member] | Unsecured Loan With Bank [Member]
Fixed Rate Interest
Notes payable at fixed rate of interest	$ 0	$ 73,825
Variable Rate Interest
Notes payable at variable rate of interest	$ 300,000	$ 0
Interest rate		2.10%
Variable rate debt due date, start	2021-10	2021-10
Variable rate debt due date, end	2023-10	2023-10
Basis spread on variable rate (as a percent)	1.40%	1.40%
Unsecured Loan With Bank [Member]
Variable Rate Interest
Interest rate		3.10%
Fixed rate debt due date		2020-03
Minimum [Member] | Notes Payable [Member]
Variable Rate Interest
Interest rate	2.80%	2.80%
Effective rate of interest	2.40%	2.00%
Maximum [Member] | Notes Payable [Member]
Variable Rate Interest
Interest rate	6.10%	6.70%
Effective rate of interest	2.80%	2.40%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Notes Payable [Member]
Variable Rate Interest
Basis spread on variable rate (as a percent)	1.60%	1.60%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Notes Payable [Member]
Variable Rate Interest
Basis spread on variable rate (as a percent)	2.00%	2.00%