Secured and unsecured senior debt Outstanding consolidated indebtedness (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	6 Months Ended
	Apr. 30, 2012	Jun. 30, 2013
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		$ 2,640,018
Unhedged Variable rate		319,406
Principal amount		2,959,424
Annual facility fee (as a percent)		0.25%
Future principal payments due on secured and unsecured debt
Unamortized discount		(2,071)
Principal amount		2,961,495
Total consolidated debt, Effective Interest		4.09%	[1]
Balloon payments		2,430,485
Principal amortization		528,939
2013
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		4,924
Unhedged Variable rate		120
Principal amount		5,044
Future principal payments due on secured and unsecured debt
Unamortized discount		(294)
Principal amount		5,338
Balloon payments		0
Principal amortization		5,044
2014
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		229,425
Unhedged Variable rate		76,240
Principal amount		305,665
Future principal payments due on secured and unsecured debt
Unamortized discount		(200)
Principal amount		305,865
Balloon payments		297,330
Principal amortization		8,335
2015
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		12,693
Unhedged Variable rate		43,046
Principal amount		55,739
Future principal payments due on secured and unsecured debt
Unamortized discount		(139)
Principal amount		55,878
Balloon payments		48,774
Principal amortization		6,965
2016
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		633,143
Unhedged Variable rate		200,000
Principal amount		833,143
Future principal payments due on secured and unsecured debt
Unamortized discount		(177)
Principal amount		833,320
Balloon payments		830,029
Principal amortization		3,114
2017
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		601,668
Unhedged Variable rate		0
Principal amount		601,668
Future principal payments due on secured and unsecured debt
Unamortized discount		(184)
Principal amount		601,852
Balloon payments		600,000
Principal amortization		1,668
Thereafter
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		1,158,165
Unhedged Variable rate		0
Principal amount		1,158,165
Future principal payments due on secured and unsecured debt
Unamortized discount		(1,077)
Principal amount		1,159,242
Balloon payments		654,352
Principal amortization		503,813
Secured Debt from Bank Maturing on 1 July 2015
Summary of fixed rate/hedged and floating rate debt
Number of extensions on line of credit		2
Secured notes payable
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		591,623
Unhedged Variable rate		119,406
Principal amount		711,029
Stated interest rate (as a percent)		5.42%
Effective rate (as a percent)		5.48%	[1]
Future principal payments due on secured and unsecured debt
2013		5,338
2014		305,615
2015		55,878
2016		233,320
2017		1,852
Thereafter		109,242
Principal amount		711,245
Secured notes payable from insurance co. maturing on 4/1/14
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)		5.26%
Effective rate (as a percent)		5.59%	[1]
Maturity date		Apr. 01, 2014	[2]
Future principal payments due on secured and unsecured debt
2013		1,945
2014		208,683
Principal amount		210,628
Secured notes payable from bank maturing on 4/20/14
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		Apr. 20, 2014	[2],[3]
Future principal payments due on secured and unsecured debt
2014		76,000
Principal amount		76,000
Secured notes payable from bank maturing on 7/1/14
Summary of fixed rate/hedged and floating rate debt
Stated interest rate (as a percent)		6.05%
Effective rate (as a percent)		4.88%	[1]
Maturity date		Jul. 01, 2014	[2]
Future principal payments due on secured and unsecured debt
2013		59
2014		6,458
Principal amount		6,517
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
2013		74
2014		7,495
Principal amount		7,569
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
2013		120
2014		240
Principal amount		360
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
2013		54
2014		138
2015		5,788
Principal amount		5,980
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
2013		814
2014		1,713
2015		1,816
2016		75,501
Principal amount		79,844
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
2013		438
2014		931
2015		988
2016		29,389
Principal amount		31,746
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
2013		1,149
2014		2,487
2015		2,652
2016		126,715
Principal amount		133,003
Secured Debt Maturing on 1 July 2017 [Member]
Summary of fixed rate/hedged and floating rate debt
Base rate		LIBOR
Applicable margin (as a percent)		1.50%
Effective rate (as a percent)		1.70%	[1]
Maturity date		Jul. 01, 2017	[2],[4]
Future principal payments due on secured and unsecured debt
2013		0
2014		0
2015		43,046
2016		0
2017		0
Thereafter		0
Principal amount		43,046
Other secured notes payable maturing on 4/1/20
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
2013		685
2014		1,453
2015		1,570
2016		1,696
2017		1,832
Thereafter		108,469
Principal amount		115,705
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
2013		0
2014		17
2015		18
2016		19
2017		20
Thereafter		773
Principal amount		847
Unsecured Senior Line of Credit and Bank Term Loans
Summary of fixed rate/hedged and floating rate debt
Effective rate (as a percent)		4.09%	[1]
$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		0
Principal amount		0
Base rate		LIBOR	[5],[6]
Applicable margin (as a percent)	1.20%	1.20%	[5],[6]
Effective rate (as a percent)		1.39%	[1],[5]
Maturity date		Apr. 30, 2017	[2],[5]
Annual facility fee (as a percent)	0.25%	0.25%
Future principal payments due on secured and unsecured debt
2013		0	[5]
2014		0	[5]
2015		0	[5]
2016		0	[5]
2017		0	[5]
Thereafter		0	[5]
Principal amount		0	[5]
2016 Unsecured Senior Bank Term Loan
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate		400,000
Unhedged Variable rate		200,000
Principal amount		600,000
Base rate		LIBOR	[5]
Applicable margin (as a percent)		1.75%	[5]
Effective rate (as a percent)		2.24%	[1],[5]
Maturity date		Jun. 30, 2016	[2],[3],[5]
Future principal payments due on secured and unsecured debt
2013		0	[5]
2014		0	[5]
2015		0	[5]
2016		600,000	[5]
2017		0	[5]
Thereafter		0	[5]
Principal amount		600,000	[5]
2017 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
Base rate		LIBOR	[5]
Applicable margin (as a percent)		1.50%	[5]
Effective rate (as a percent)		3.93%	[1],[5]
Maturity date		Jan. 31, 2017	[2],[3],[5]
Future principal payments due on secured and unsecured debt
2013		0	[5]
2014		0	[5]
2015		0	[5]
2016		0	[5]
2017		600,000	[5]
Thereafter		0	[5]
Principal amount		600,000	[5]
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
2013		0
2014		250
2015		0
2016		0
2017		0
Thereafter		550,000
Principal amount		550,250
Unsecured Senior Notes 2023 [Member]
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]
Future principal payments due on secured and unsecured debt
2013		0
2014		0
2015		0
2016		0
2017		0
Thereafter		500,000
Principal amount		$ 500,000

[1] Represents the weighted average contractual 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] This loan may be prepaid without any prepayment penalty.

[4] We have two, one year options to extend the stated maturity date of July 1, 2015.

[5] Does not reflect amendments completed or in progress subsequent to June 30, 2013, that will reduce our borrowing costs and/or extend our maturity as noted in our Subsequent Events note to the consolidated financial statements. See Note 13 for amended terms.

[6] In addition to the stated rate, we were subject to an annual facility fee of 0.25% as of June 30, 2013.