Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 4) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Nov. 30, 2017	Feb. 28, 2017	Dec. 31, 2017	Jun. 30, 2017	May 31, 2017	Dec. 31, 2016
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes			$ 7,404,313			$ 7,076,758
Percentage of principle amount at which the entity may redeem some or all of the notes			100.00%
Variable Rate Unsecured Term Loan $100 Million [Member] | LIBOR
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)		0.90%
Variable Rate Unsecured Term Loan $150 Million [Member] | LIBOR
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)		1.50%
Unsecured notes
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes			$ 5,900,000
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 6.100 Percent Maturities 2020
Mortgage 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
Mortgage 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
Mortgage 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 | Floating Rate Unsecured Notes 300 Million [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes			$ 300,000
Unsecured notes | Floating Rate Unsecured Notes 300 Million [Member] | LIBOR
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, basis spread on variable rate (as a percent)	0.43%		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 of unsecured notes (as a percent)			2.95%
Unsecured notes | Variable Rate Unsecured Term Loan $100 Million [Member]
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 [Member] | 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 of unsecured notes (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 of unsecured notes (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 of unsecured notes (as a percent)			3.50%
Unsecured notes | Variable Rate Unsecured Term Loan $150 Million [Member]
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 [Member] | 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 [Member]
Mortgage 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]
Mortgage 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 [Member]
Mortgage 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 [Member]
Mortgage 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 [Member]
Mortgage 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 [Member]
Mortgage 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 [Member]
Mortgage 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]
Mortgage 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%
Secured notes
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			$ 192,304
Mortgage notes payable and unsecured notes			1,312,009
Secured notes | Notes payable maturing in 2017
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Stated interest rate of unsecured notes (as a percent)					6.256%
Secured notes | Notes payable maturing in 2018
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			7,258
Mortgage notes payable and unsecured notes			76,663
Secured notes | Notes payable maturing in 2019
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			4,696
Mortgage notes payable and unsecured notes			114,721
Stated interest rate of unsecured notes (as a percent)				5.86%
Secured notes | Notes Payable Maturities 2020 [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			3,624
Mortgage notes payable and unsecured notes			140,429
Secured notes | Notes payable maturing in 2021
Mortgage 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
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			3,795
Secured notes | Notes Payable Maturities 2023 [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			4,040
Secured notes | Notes Payable 2024
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			4,310
Secured notes | Notes Payable Maturities 2025 [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			4,585
Mortgage notes payable and unsecured notes			84,835
Secured notes | Notes Payable Maturities 2026 [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			4,894
Secured notes | Notes Payable Maturities 2027 [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			3,083
Mortgage notes payable and unsecured notes			185,100
Stated interest rate of unsecured notes (as a percent)					3.61%
Secured notes | Notes Payable Maturities Thereafter [Member]
Mortgage Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			148,468
Mortgage notes payable and unsecured notes			$ 682,417