Secured and unsecured senior debt Detail of secured and unsecured debt (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	$ 3,275,629
Unhedged Variable rate	1,038,603
Total Consolidated	4,314,232
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	4,279,969
Debt Instrument, Annual Principal Payment	$ 34,263
Effective rate (as a percent)	2.97%	[1]
2015
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	$ 2,282
Unhedged Variable rate	0
Total Consolidated	2,282
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	0
Debt Instrument, Annual Principal Payment	2,282
2016
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	241,973
Unhedged Variable rate	68,099
Total Consolidated	310,072
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	304,999
Debt Instrument, Annual Principal Payment	5,073
2017
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	3,615
Unhedged Variable rate	227,504
Total Consolidated	231,119
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	227,504
Debt Instrument, Annual Principal Payment	3,615
2018
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	4,932
Unhedged Variable rate	0
Total Consolidated	4,932
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	0
Debt Instrument, Annual Principal Payment	4,932
2019 [Member]
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	705,578
Unhedged Variable rate	743,000
Total Consolidated	1,448,578
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	1,443,000
Debt Instrument, Annual Principal Payment	5,578
Maturity Date After 2019 [Member]
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	2,317,249
Unhedged Variable rate	0
Total Consolidated	2,317,249
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	2,304,466
Debt Instrument, Annual Principal Payment	12,783
Secured notes payable
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	478,016
Unhedged Variable rate	295,603
Total Consolidated	$ 773,619
Stated interest rate (as a percent)	4.35%
Effective rate (as a percent)	4.23%	[1]
Future principal payments due on secured and unsecured debt
Due Current Year	$ (2,365)
Due Next Year	310,409
Due Year Three	231,469
Due Year Four	5,294
Due Year Five	5,953
Thereafter	$ 218,129
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 466
Future principal payments due on secured and unsecured debt
Due Next Year	75,501
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 75,967
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 249
Future principal payments due on secured and unsecured debt
Due Next Year	29,389
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 29,638
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 45
Future principal payments due on secured and unsecured debt
Due Next Year	6,916
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 6,961
Secured notes payable maturing on 06/1/16
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.59%	[1]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	20,714
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 20,714
Secured Debt from Bank Maturing on 1 July 2016 [Member]
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.69%	[1]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	47,385
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	$ 0
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 662
Future principal payments due on secured and unsecured debt
Due Next Year	126,715
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 127,377
Secured Debt from Bank Maturing on 20 January 2017
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	2.18%
Effective rate (as a percent)	2.18%	[1]
Maturity Date	Jan. 20, 2017	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	76,000
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 76,000
Secured Debt Maturing on 23 August 2017 [Member]
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)	1.54%	[1]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	151,504
Due Year Four	0
Due Year Five	0
Thereafter	0
Outstanding Balance	$ 151,504
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 404
Future principal payments due on secured and unsecured debt
Due Next Year	1,696
Due Year Three	1,832
Due Year Four	1,979
Due Year Five	2,138
Thereafter	104,352
Outstanding Balance	$ 112,401
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 354
Future principal payments due on secured and unsecured debt
Due Next Year	1,464
Due Year Three	1,540
Due Year Four	1,614
Due Year Five	1,692
Thereafter	31,674
Outstanding Balance	$ 38,338
Secured debt maturing in 2023 [Member]
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	3.93%
Effective rate (as a percent)	3.10%	[1]
Maturity Date	Mar. 10, 2023	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	1,091
Due Year Five	1,505
Thereafter	79,404
Outstanding Balance	$ 82,000
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	Jul. 01, 2036	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 1
Future principal payments due on secured and unsecured debt
Due Next Year	19
Due Year Three	20
Due Year Four	22
Due Year Five	23
Thereafter	728
Outstanding Balance	813
Unamortized Premiums
Future principal payments due on secured and unsecured debt
Unamortized premium	4,521
Unamortized Premiums | 2015
Future principal payments due on secured and unsecured debt
Unamortized premium	184
Unamortized Premiums | 2016
Future principal payments due on secured and unsecured debt
Unamortized premium	610
Unamortized Premiums | 2017
Future principal payments due on secured and unsecured debt
Unamortized premium	573
Unamortized Premiums | 2018
Future principal payments due on secured and unsecured debt
Unamortized premium	588
Unamortized Premiums | 2019 [Member]
Future principal payments due on secured and unsecured debt
Unamortized premium	595
Unamortized Premiums | Maturity Date After 2019 [Member]
Future principal payments due on secured and unsecured debt
Unamortized premium	1,971
Unsecured Debt
Summary of fixed rate/hedged and floating rate debt
Total Consolidated	$ 3,540,613
Effective rate (as a percent)	2.69%	[1]
Unsecured Debt | 2015
Future principal payments due on secured and unsecured debt
Due Current Year	$ 83
Unsecured Debt | 2016
Future principal payments due on secured and unsecured debt
Due Next Year	(337)
Unsecured Debt | 2017
Future principal payments due on secured and unsecured debt
Due Year Three	(350)
Unsecured Debt | 2018
Future principal payments due on secured and unsecured debt
Due Year Four	(362)
Unsecured Debt | 2019 [Member]
Future principal payments due on secured and unsecured debt
Due Year Five	1,442,625
Unsecured Debt | Maturity Date After 2019 [Member]
Future principal payments due on secured and unsecured debt
Thereafter	2,099,120
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
Total Consolidated	$ 600,000
Effective rate (as a percent)	1.72%	[1]
Maturity Date	Jan. 03, 2019	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	600,000
Thereafter	0
Outstanding Balance	600,000
Unsecured Bank Term Loan 2021 [Member]
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	350,000
Unhedged Variable rate	0
Total Consolidated	$ 350,000
Effective rate (as a percent)	1.52%	[1]
Maturity Date	Jan. 15, 2021	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	350,000
Outstanding Balance	350,000
$1.5 billion unsecured senior line of credit
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	100,000
Unhedged Variable rate	743,000
Total Consolidated	$ 843,000
Effective rate (as a percent)	1.19%	[1],[3]
Maturity Date	Jan. 03, 2019	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Annual facility fee (as a percent)	0.20%
Future principal payments due on secured and unsecured debt
Due Next Year	$ 0
Due Year Three	0
Due Year Four	0
Due Year Five	843,000
Thereafter	0
Outstanding Balance	$ 843,000
Unsecured Senior Notes Due in January 2020 [Member]
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	2.75%
Effective rate (as a percent)	2.79%	[1]
Maturity Date	Jan. 15, 2020	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	400,000
Outstanding Balance	$ 400,000
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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	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]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	500,000
Outstanding Balance	$ 500,000
Unsecured Senior Notes Due in July 2029 [Member]
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)	4.50%
Effective rate (as a percent)	4.51%	[1]
Maturity Date	Jul. 30, 2029	[2]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Future principal payments due on secured and unsecured debt
Due Next Year	0
Due Year Three	0
Due Year Four	0
Due Year Five	0
Thereafter	300,000
Outstanding Balance	300,000
Unamortized Discounts
Future principal payments due on secured and unsecured debt
Unamortized discount	(2,387)
Unamortized Discounts | 2015
Future principal payments due on secured and unsecured debt
Unamortized discount	(83)
Unamortized Discounts | 2016
Future principal payments due on secured and unsecured debt
Unamortized discount	(337)
Unamortized Discounts | 2017
Future principal payments due on secured and unsecured debt
Unamortized discount	(350)
Unamortized Discounts | 2018
Future principal payments due on secured and unsecured debt
Unamortized discount	(362)
Unamortized Discounts | 2019 [Member]
Future principal payments due on secured and unsecured debt
Unamortized discount	(375)
Unamortized Discounts | Maturity Date After 2019 [Member]
Future principal payments due on secured and unsecured debt
Unamortized discount	(880)
Senior Notes [Member]
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	1,747,613
Unhedged Variable rate	0
Total Consolidated	$ 1,747,613
Effective rate (as a percent)	3.98%
LIBOR | Secured notes payable maturing on 06/1/16
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Applicable margin (as a percent)	1.40%
LIBOR | Secured Debt Maturing on 23 August 2017 [Member]
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Applicable margin (as a percent)	1.35%
LIBOR | 2019 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Applicable margin (as a percent)	1.20%
LIBOR | Unsecured Bank Term Loan 2021 [Member]
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Applicable margin (as a percent)	1.10%
LIBOR | $1.5 billion unsecured senior line of credit
Summary of fixed rate/hedged and floating rate debt
Base rate	LIBOR
Applicable margin (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] Our unsecured senior line of credit contains a feature that allows lenders to competitively bid on the interest rate for borrowings under the facility. This may result in an interest rate that is below the stated rate of LIBOR+1.10%. In addition to the cost of borrowing, the facility is subject to an annual facility fee of 0.20%, based on the aggregate commitments outstanding.

[4] We have two, one-year options to extend the stated maturity date to June 1, 2018, subject to certain conditions.