Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 7,102,355	$ 7,404,313
Percentage of principle amount at which the entity may redeem some or all of the notes	100.00%
Unsecured notes
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 5,950,000
Unsecured notes | Minimum
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.20%
Unsecured notes | Maximum
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.45%
Unsecured notes | Notes Payable 3.625 Maturities 2020
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 400,000
Stated interest rate (as a percent)	3.625%
Unsecured notes | Notes payable maturing in 2021
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate (as a percent)	3.95%
Unsecured notes | Floating Rate Unsecured Notes 300 Million
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Unsecured notes | Floating Rate Unsecured Notes 300 Million | LIBOR
Mortgage 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
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 450,000
Stated interest rate (as a percent)	2.95%
Unsecured notes | Variable Rate Unsecured Term Loan $100 Million
Mortgage 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
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.90%
Unsecured notes | Notes Payable 4.200 Maturities 2023
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate (as a percent)	4.20%
Unsecured notes | Notes Payable 2.850 Maturities 2023
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate (as a percent)	2.85%
Unsecured notes | Notes Payable 2024
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate (as a percent)	3.50%
Unsecured notes | Variable Rate Unsecured Term Loan $150 Million
Mortgage 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
Mortgage 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
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 525,000
Stated interest rate (as a percent)	3.45%
Unsecured notes | Notes Payable 3.500 Maturities 2025
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate (as a percent)	3.50%
Unsecured notes | Notes Payable 2.950 Maturities 2026
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 475,000
Stated interest rate (as a percent)	2.95%
Unsecured notes | Notes Payable 2.900 Maturities 2026
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate (as a percent)	2.90%
Unsecured notes | Notes Payable Maturities 2027
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 400,000
Stated interest rate (as a percent)	3.35%
Unsecured notes | Notes Payable Maturities 2028
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 450,000
Stated interest rate (as a percent)	3.20%
Unsecured notes | Notes Payable Maturities 2046
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate (as a percent)	3.90%
Unsecured notes | Notes Payable Maturities 2047
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate (as a percent)	4.15%
Unsecured notes | Notes Payable Maturities 2048
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate (as a percent)	4.35%
Secured notes
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	$ 55,075
Mortgage notes payable and unsecured notes	1,097,280
Secured notes | Notes payable maturing in 2019
Mortgage 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
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,682
Mortgage notes payable and unsecured notes	140,430
Secured notes | Notes payable maturing in 2021
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,204
Mortgage notes payable and unsecured notes	27,844
Secured notes | Notes payable maturing in 2022
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,318
Secured notes | Notes Payable Maturities 2023
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,439
Secured notes | Notes Payable 2024
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,577
Secured notes | Notes Payable Maturities 2025
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,708
Mortgage notes payable and unsecured notes	84,835
Secured notes | Notes Payable Maturities 2026
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,845
Secured notes | Notes Payable Maturities 2027
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	2,270
Mortgage notes payable and unsecured notes	185,100
Secured notes | Notes Payable Maturities 2028
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	912
Mortgage notes payable and unsecured notes	0
Secured notes | Notes Payable Maturities Thereafter
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	30,296
Mortgage notes payable and unsecured notes	$ 544,349