Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 3) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Apr. 30, 2018	Feb. 28, 2018	Dec. 31, 2017
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 7,547,792			$ 7,404,313
Secured notes
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	156,712
Mortgage notes payable and unsecured notes	1,191,080
Secured notes | Notes Payable Maturities 2018
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	1,638
Mortgage notes payable and unsecured notes	0
Stated interest rate of unsecured notes (as a percent)		3.06%	4.61%
Secured notes | Notes Payable Maturities 2019
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,824
Mortgage notes payable and unsecured notes	114,722
Secured notes | Notes Payable Maturities 2020
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,682
Mortgage notes payable and unsecured notes	140,430
Secured notes | Notes Payable Maturities 2021
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,549
Mortgage notes payable and unsecured notes	27,844
Secured notes | Notes payable maturing in 2022
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,723
Secured notes | Notes Payable Maturities 2023
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,899
Secured notes | Notes Payable Maturities 2024
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,077
Secured notes | Notes Payable Maturities 2025
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,268
Mortgage notes payable and unsecured notes	84,835
Secured notes | Notes Payable Maturities 2026
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,485
Secured notes | Notes Payable Maturities 2027
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,974
Mortgage notes payable and unsecured notes	185,100
Secured notes | Notes Payable Maturities Thereafter
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	127,593
Mortgage notes payable and unsecured notes	638,149
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	6,200,000
Unsecured notes | Notes Payable 6.100 Percent Maturities 2020
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	6.10%
Unsecured notes | Notes Payable 3.625 Percent Maturities 2020
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 400,000
Stated interest rate of unsecured notes (as a percent)	3.625%
Unsecured notes | Notes Payable Maturities 2021
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	3.95%
Unsecured notes | Variable Rate Unsecured Term Loan $300 Million
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Unsecured notes | Variable Rate Unsecured Term Loan $300 Million | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.43%
Unsecured notes | Notes payable maturing in 2022
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 450,000
Stated interest rate of unsecured notes (as a percent)	2.95%
Unsecured notes | Variable Rate Unsecured Term Loan $100 Million
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 100,000
Unsecured notes | Variable Rate Unsecured Term Loan $100 Million | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.90%
Unsecured notes | Notes payable maturing in 2023
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate of unsecured notes (as a percent)	4.20%
Unsecured notes | Notes Payable 2.850 Maturities 2023
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	2.85%
Unsecured notes | Notes Payable Maturities 2024
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	3.50%
Unsecured notes | Variable Rate Unsecured Term Loan $150 Million
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 150,000
Unsecured notes | Variable Rate Unsecured Term Loan $150 Million | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	1.50%
Unsecured notes | Notes Payable 3.450 Maturities 2025
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 525,000
Stated interest rate of unsecured notes (as a percent)	3.45%
Unsecured notes | Notes Payable 3.500 Maturities 2025
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	3.50%
Unsecured notes | Notes Payable 2.950 Maturities 2026
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 475,000
Stated interest rate of unsecured notes (as a percent)	2.95%
Unsecured notes | Notes Payable 2.900 Maturities 2026
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	2.90%
Unsecured notes | Notes Payable Maturities 2027
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 400,000
Stated interest rate of unsecured notes (as a percent)	3.35%
Unsecured notes | Notes Payable Maturities 2046
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate of unsecured notes (as a percent)	3.90%
Unsecured notes | Notes Payable Maturities 2047
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	4.15%
Unsecured notes | Notes Payable Maturities 2028 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 450,000
Stated interest rate of unsecured notes (as a percent)	3.20%
Unsecured notes | Notes Payable Maturities 2048 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	4.35%