Secured and unsecured senior debt Detail of secured and unsecured debt (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	$ 2,413,965
Unhedged Variable rate	920,896
Principal amount	3,334,861
Total consolidated debt, Effective Interest	3.03%	[1]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	3,300,992
Debt Instrument, Annual Principal Payment	33,869
Future principal payments due on secured and unsecured debt
Repayments of Unsecured Debt	0		150,000
Percentage of unhedged floating rate total debt	28.00%
2014
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	11,583
Unhedged Variable rate	120
Principal amount	11,703
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	7,339
Debt Instrument, Annual Principal Payment	4,364
2015
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	14,446
Unhedged Variable rate	46,399
Principal amount	60,845
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	52,139
Debt Instrument, Annual Principal Payment	8,706
2016
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	591,582
Unhedged Variable rate	161,937
Principal amount	753,519
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	748,836
Debt Instrument, Annual Principal Payment	4,683
2017
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	3,208
Unhedged Variable rate	141,440
Principal amount	144,648
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	141,440
Debt Instrument, Annual Principal Payment	3,208
2018
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	3,423
Unhedged Variable rate	0
Principal amount	3,423
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	0
Debt Instrument, Annual Principal Payment	3,423
Thereafter
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	1,789,723
Unhedged Variable rate	571,000
Principal amount	2,360,723
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	2,351,238
Debt Instrument, Annual Principal Payment	9,485
Secured notes payable
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	415,655
Unhedged Variable rate	199,896
Principal amount	615,551
Stated interest rate (as a percent)	4.89%
Effective rate (as a percent)	4.83%	[1]
Future principal payments due on secured and unsecured debt
2014	11,785
2015	61,015
2016	253,696
2017	144,832
2018	3,615
Thereafter	140,608
Secured notes payable from bank maturing on 11/1/14
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	5.39%
Effective rate (as a percent)	4.00%	[1]
Maturity Date	Nov. 01, 2014	[2]
Future principal payments due on secured and unsecured debt
2014	7,386
2015	0
2016	0
2017	0
2018	0
Thereafter	0
Outstanding Balance	7,386
Other secured notes payable maturing on 11/18/14
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	6.00%
Effective rate (as a percent)	6.00%	[1]
Maturity Date	Nov. 18, 2014	[2]
Future principal payments due on secured and unsecured debt
2014	120
2015	0
2016	0
2017	0
2018	0
Thereafter	0
Outstanding Balance	120
Secured notes payable from bank maturing on 6/1/15
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	5.64%
Effective rate (as a percent)	4.50%	[1]
Maturity Date	Jun. 01, 2015	[2]
Future principal payments due on secured and unsecured debt
2014	69
2015	5,777
2016	0
2017	0
2018	0
Thereafter	0
Outstanding Balance	5,846
Secured notes payable maturing on 7/1/15
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.66%	[1]
Maturity Date	Jul. 01, 2015	[2]
Number of extensions available under line of credit	2
Future principal payments due on secured and unsecured debt
2014	0
2015	46,399
2016	0
2017	0
2018	0
Thereafter	0
Outstanding Balance	46,399
CMBS maturing on 1/1/16
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	5.73%
Effective rate (as a percent)	5.73%	[1]
Maturity Date	Jan. 01, 2016	[2]
Future principal payments due on secured and unsecured debt
2014	862
2015	1,816
2016	75,501
2017	0
2018	0
Thereafter	0
Outstanding Balance	78,179
CMBS maturing on 4/1/16
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	5.82%
Effective rate (as a percent)	5.82%	[1]
Maturity Date	Apr. 01, 2016	[2]
Future principal payments due on secured and unsecured debt
2014	465
2015	988
2016	29,389
2017	0
2018	0
Thereafter	0
Outstanding Balance	30,842
Secured Debt Maturing On 15 April 2016
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	5.74%
Effective rate (as a percent)	3.00%	[1]
Maturity Date	Apr. 15, 2016	[2]
Future principal payments due on secured and unsecured debt
2014	83
2015	175
2016	6,916
2017	0
2018	0
Thereafter	0
Outstanding Balance	7,174
Secured notes payable maturing on 06/1/16
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.56%	[1]
Maturity Date	Jun. 01, 2016	[2]
Number of extensions available under line of credit	2
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	11,936
2017	0
2018	0
Thereafter	0
Outstanding Balance	11,936
CMBS maturing on 8/1/16
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	6.35%
Effective rate (as a percent)	6.35%	[1]
Maturity Date	Aug. 01, 2016	[2]
Future principal payments due on secured and unsecured debt
2014	1,229
2015	2,652
2016	126,715
2017	0
2018	0
Thereafter	0
Outstanding Balance	130,596
Secured Debt from Bank Maturing on 20 January 2017
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	2.14%
Effective rate (as a percent)	2.14%	[1]
Maturity Date	Jan. 20, 2017	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	76,000
2018	0
Thereafter	0
Outstanding Balance	76,000
Secured notes payable maturing on 8/23/17
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.50%	[1]
Maturity Date	Aug. 23, 2017	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	65,440
2018	0
Thereafter	0
Outstanding Balance	65,440
Secured Debt Other Maturing 1 April 2020
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	7.75%
Effective rate (as a percent)	7.75%	[1]
Maturity Date	Apr. 01, 2020	[2]
Future principal payments due on secured and unsecured debt
2014	741
2015	1,570
2016	1,696
2017	1,832
2018	1,979
Thereafter	106,490
Outstanding Balance	114,308
Secured Debt Maturing on January 2023
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	4.66%
Effective rate (as a percent)	4.66%	[1]
Maturity Date	Jan. 01, 2023	[2]
Future principal payments due on secured and unsecured debt
2014	669
2015	1,402
2016	1,464
2017	1,540
2018	1,614
Thereafter	33,367
Outstanding Balance	40,056
Secured notes payable from bank maturing on 6/1/37
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	6.50%
Effective rate (as a percent)	6.50%	[1]
Maturity Date	Jun. 01, 2037	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	18
2016	19
2017	20
2018	22
Thereafter	751
Outstanding Balance	830
Unamortized Premiums
Future principal payments due on secured and unsecured debt
Unamortized premium	439
Unamortized Premiums | 2014
Future principal payments due on secured and unsecured debt
Unamortized premium	161
Unamortized Premiums | 2015
Future principal payments due on secured and unsecured debt
Unamortized premium	218
Unamortized Premiums | 2016
Future principal payments due on secured and unsecured debt
Unamortized premium	60
Unamortized Premiums | 2017
Future principal payments due on secured and unsecured debt
Unamortized premium	0
Unamortized Premiums | 2018
Future principal payments due on secured and unsecured debt
Unamortized premium	0
Unamortized Premiums | Thereafter
Future principal payments due on secured and unsecured debt
Unamortized premium	0
Unsecured Debt
Summary of fixed rate/hedged and floating rate debt
Principal amount	2,719,310
Effective rate (as a percent)	2.63%	[1]
Unsecured Debt | 2014
Future principal payments due on secured and unsecured debt
2014	(82)
Unsecured Debt | 2015
Future principal payments due on secured and unsecured debt
2015	(170)
Unsecured Debt | 2016
Future principal payments due on secured and unsecured debt
2016	499,823
Unsecured Debt | 2017
Future principal payments due on secured and unsecured debt
2017	(184)
Unsecured Debt | 2018
Future principal payments due on secured and unsecured debt
2018	(192)
Unsecured Debt | Thereafter
Future principal payments due on secured and unsecured debt
Thereafter	2,220,115
2016 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	350,000
Unhedged Variable rate	150,000
Principal amount	500,000	[3]
Effective rate (as a percent)	1.40%	[1]
Maturity Date	Jul. 31, 2016	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	500,000
2017	0
2018	0
Thereafter	0
Outstanding Balance	500,000
2019 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	600,000
Unhedged Variable rate	0
Principal amount	600,000
Effective rate (as a percent)	2.05%	[1]
Maturity Date	Jan. 03, 2019	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	0
2018	0
Thereafter	600,000
Outstanding Balance	600,000
$1.5 billion unsecured senior line of credit
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	0
Unhedged Variable rate	571,000
Principal amount	571,000	[3]
Effective rate (as a percent)	1.25%	[1]
Maturity Date	Jan. 03, 2019	[2]
Annual facility fee (as a percent)	0.20%
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	0
2018	0
Thereafter	571,000
Outstanding Balance	571,000
4.60% unsecured senior notes payable
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	4.60%
Effective rate (as a percent)	4.61%	[1]
Maturity Date	Apr. 01, 2022	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	0
2018	0
Thereafter	550,000
Outstanding Balance	550,000
3.90% unsecured senior notes payable
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	3.90%
Effective rate (as a percent)	3.94%	[1]
Maturity Date	Jun. 15, 2023	[2]
Future principal payments due on secured and unsecured debt
2014	0
2015	0
2016	0
2017	0
2018	0
Thereafter	500,000
Outstanding Balance	500,000
Unamortized Discounts
Future principal payments due on secured and unsecured debt
Unamortized discount	(1,690)
Unamortized Discounts | 2014
Future principal payments due on secured and unsecured debt
Unamortized discount	(82)
Unamortized Discounts | 2015
Future principal payments due on secured and unsecured debt
Unamortized discount	(170)
Unamortized Discounts | 2016
Future principal payments due on secured and unsecured debt
Unamortized discount	(177)
Unamortized Discounts | 2017
Future principal payments due on secured and unsecured debt
Unamortized discount	(184)
Unamortized Discounts | 2018
Future principal payments due on secured and unsecured debt
Unamortized discount	(192)
Unamortized Discounts | Thereafter
Future principal payments due on secured and unsecured debt
Unamortized discount	(885)
Senior Notes [Member]
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	1,048,310
Unhedged Variable rate	0
Principal amount	$ 1,048,310
Effective rate (as a percent)	4.29%	[1]
LIBOR | Secured notes payable maturing on 7/1/15
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.50%
LIBOR | Secured notes payable maturing on 06/1/16
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.40%
LIBOR | Secured notes payable maturing on 8/23/17
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.35%
LIBOR | 2016 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.20%
LIBOR | 2019 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.20%
LIBOR | $1.5 billion unsecured senior line of credit
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Basis spread on LIBOR (as a percent)	1.10%	[4]

[1] Represents the weighted average interest rate as of the end of the period plus the impact of debt premiums/discounts and our interest rate swap agreements. The weighted average interest rate excludes bank fees and amortization of loan fees.

[2] Includes any extension options that we control.

[3] These amounts do not reflect our unsecured senior notes payable offering completed on July 18, 2014. Net proceeds of $694 million were used to reduce variable-rate debt, including the partial repayment of $125 million of our 2016 Unsecured Senior Bank Term Loan and the reduction of $569 million of borrowings outstanding on our unsecured senior line of credit. See Note 13 – Subsequent Events, to our consolidated financial statements (unaudited) appearing elsewhere in this quarterly report on Form 10-Q for further information.

[4] In addition to the stated rate, the unsecured senior line of credit is subject to an annual facility fee of 0.20%.