Real Estate and Other Assets Held For Sale and Discontinued Operations (Details) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015 USD ($) ft²		Sep. 30, 2015 USD ($)	[1]	Jun. 30, 2015 USD ($)	[1]	Mar. 31, 2015 USD ($)	[1]	Dec. 31, 2014 USD ($)		Sep. 30, 2014 USD ($)	[1]	Jun. 30, 2014 USD ($)	[1]	Mar. 31, 2014 USD ($)	[1]	Dec. 31, 2015 USD ($) ft²	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable square feet of commercial real estate (in square feet) | ft²	32,486,000																32,486,000
Rentable square feet of commercial real estate under development (in square feet) | ft²	1,454,200																1,454,200
Assets, held for sale [Abstract]
Land	$ 16,681								$ 16,406								$ 16,681	$ 16,406
Building and tenant improvements	322,811								313,323								322,811	313,323
Development in-process	0								4,562								0	4,562
Land held for development	1,089								2,084								1,089	2,084
Less accumulated depreciation	(131,274)								(131,419)								(131,274)	(131,419)
Net real estate assets	209,307								204,956								209,307	204,956
Accrued straight-line rents receivable, net	11,730								11,643								11,730	11,643
Deferred leasing costs, net	6,690								6,320								6,690	6,320
Prepaid expenses and other assets	13,221								13,896								13,221	13,896
Real estate and other assets, net, held for sale	240,948								236,815								240,948	236,815
Liabilities [Abstract]
Accounts payable, accrued expenses and other liabilities	(6,717)								(6,151)								(6,717)	(6,151)
Financing obligation	(7,402)								(8,962)								(7,402)	(8,962)
Liabilities held for sale	(14,119)								(15,113)								(14,119)	(15,113)
Discontinued Operations [Abstract]
Rental and other revenues																	50,935	52,597	$ 72,614
Operating expenses:
Rental property and other expenses																	20,805	19,620	27,440
Depreciation and amortization																	14,039	15,386	19,773
General and administrative																	2,366	965	812
Total operating expenses																	37,210	35,971	48,025
Interest expense																	621	725	817
Other income																	2,635	2,700	3,086
Income from discontinued operations																	15,739	18,601	26,858
Impairments of real estate assets																	0	0	(2,194)
Net gains on disposition of discontinued operations																	0	384	63,792
Total income from discontinued operations	$ 2,889	[1]	$ 4,265		$ 4,670		$ 3,915		$ 5,434	[1]	$ 4,816		$ 4,138		$ 4,597		15,739	18,985	88,456
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Cash flows from operating activities																	27,579	32,485	32,644
Cash flows from investing activities																	$ (16,445)	$ (8,279)	$ (7,482)
Office Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable square feet of commercial real estate (in square feet) | ft²	468,000																468,000
Retail Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable square feet of commercial real estate (in square feet) | ft²	776,000																776,000
Rentable square feet of commercial real estate under development (in square feet) | ft²	28,000																28,000

[1] As a result of discontinued operations, the amounts presented may not equal the amounts previously reported in the most recent Form 10-Qs or prior 10-K for each period. Below is a reconciliation to the amounts previously reported: Quarter Ended March 31, June 30, September 30, 2015 2015 2015Rental and other revenues, as reported$157,310 $161,136 $163,736Discontinued operations(12,074) (12,593) (12,970)Rental and other revenues, as adjusted$145,236 $148,543 $150,766Income from continuing operations, as reported$20,835 $26,891 $31,617Discontinued operations(3,915) (4,670) (4,265)Income from continuing operations, as adjusted$16,920 $22,221 $27,352Income from discontinued operations, as reported$— $— $—Additional discontinued operations from properties sold subsequent to the respective reporting period3,915 4,670 4,265Income from discontinued operations, as adjusted$3,915 $4,670 $4,265 Quarter Ended March 31, June 30, September 30, December 31, 2014 2014 2014 2014Rental and other revenues, as reported$148,453 $152,722 $152,629 $154,664Discontinued operations(12,632) (12,766) (13,259) (13,940)Rental and other revenues, as adjusted$135,821 $139,956 $139,370 $140,724Income from continuing operations, as reported$13,192 $24,512 $54,299 $23,585Discontinued operations(4,213) (4,138) (4,816) (5,434)Income from continuing operations, as adjusted$8,979 $20,374 $49,483 $18,151Income from discontinued operations, as reported$384 $— $— $—Additional discontinued operations from properties sold subsequent to the respective reporting period4,213 4,138 4,816 5,434Income from discontinued operations, as adjusted$4,597 $4,138 $4,816 $5,434