Notes Payable, Unsecured Notes and Credit Facility (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 6,528,834	$ 6,481,291
Secured notes
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	292,807
Mortgage notes payable and unsecured notes	2,361,027
Secured notes | Notes Payable Maturities 2016 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	12,156
Mortgage notes payable and unsecured notes	0
Secured notes | Notes Payable Maturities 2017 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	17,166
Mortgage notes payable and unsecured notes	709,791
Secured notes | Notes Payable Maturities 2018 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	16,236
Mortgage notes payable and unsecured notes	76,950
Secured notes | Notes payable maturing in 2019
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,696
Mortgage notes payable and unsecured notes	588,429
Secured notes | Notes Payable Maturities 2020 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,624
Mortgage notes payable and unsecured notes	118,729
Secured notes | Notes Payable Maturities 2021 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,551
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	3,795
Secured notes | Notes payable maturing in 2023
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,040
Secured notes | Notes Payable Maturities 2024 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,310
Secured notes | Notes Payable Maturities 2025 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,553
Mortgage notes payable and unsecured notes	84,835
Secured notes | Notes payable with maturities after 2023
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	218,680
Mortgage notes payable and unsecured notes	754,449
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	3,875,000
Unsecured notes | Notes Payable Maturities 2016 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	5.75%
Unsecured notes | Notes Payable Maturities 2017 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	5.70%
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 maturing in 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 | Term Loan
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Unsecured notes | Term Loan | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	1.45%
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 | 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 [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)	3.50%
Unsecured notes | Notes Payable 3.450 Maturities 2025 [Member]
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 [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)	3.50%
Unsecured notes | Notes payable with maturities after 2023
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 0