Capital and Financing Transactions Interest Rate Swaps (Details) (USD $)			9 Months Ended		9 Months Ended			9 Months Ended			9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended		0 Months Ended	9 Months Ended			9 Months Ended				9 Months Ended						0 Months Ended			6 Months Ended			0 Months Ended
	Sep. 30, 2013 sqft	Sep. 30, 2012	Sep. 30, 2013 Swap 1 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 1 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 3 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 3 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 3 Receivables and Other Assets	Sep. 30, 2013 Swap 4 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 4 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 4 Receivables and Other Assets	Sep. 30, 2013 Swap 5 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 5 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 11 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 11 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 6 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 6 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 7 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 7 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 12 Accounts Payable and Other Liabilities	Jun. 12, 2013 Swap 12 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 12 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 8 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 8 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 9 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 9 Accounts Payable and Other Liabilities	May 31, 2013 Swap 13 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 13 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 13 Accounts Payable and Other Liabilities	Sep. 30, 2013 Swap 13 Receivables and Other Assets	Sep. 30, 2013 Swap 10 Accounts Payable and Other Liabilities	Sep. 30, 2012 Swap 10 Accounts Payable and Other Liabilities	Sep. 30, 2013 Unsecured Term Loan $120 million Wells Fargo Bank	Jun. 12, 2013 Unsecured Term Loan $120 million Wells Fargo Bank	Sep. 30, 2013 Unsecured Term Loan $120 million Wells Fargo Bank Swap 12 Accounts Payable and Other Liabilities	Sep. 30, 2013 Unsecured Term Loan $125 million Key Bank	Mar. 25, 2013 Fund II Assets Swap	Sep. 30, 2013 Hayden Ferry Lakeside II sqft	Jun. 28, 2013 Hayden Ferry Lakeside II sqft	Mar. 25, 2013 Tampa Fund II Assets sqft	Aug. 03, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II	Jun. 28, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II	Aug. 01, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II	Jun. 27, 2013 Hayden Ferry II Original Mortgage Hayden Ferry Lakeside II	Jun. 28, 2013 Hayden Ferry II Original Mortgage Hayden Ferry Lakeside II	Sep. 30, 2013 LIBOR Unsecured Term Loan $125 million	Jun. 28, 2013 LIBOR Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II	Sep. 30, 2013 Minimum LIBOR Unsecured Term Loan $120 million	Sep. 30, 2013 Minimum LIBOR Unsecured Term Loan $125 million	Jun. 28, 2013 Minimum LIBOR Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II	Sep. 30, 2013 Maximum LIBOR Unsecured Term Loan $120 million	Sep. 30, 2013 Maximum LIBOR Unsecured Term Loan $125 million	Jun. 28, 2013 Maximum LIBOR Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II
Derivative [Line Items]
Notional amount			$ 12,088,000		$ 50,000,000			$ 75,000,000			$ 33,875,000		$ 625,000		$ 22,000,000		$ 46,250,000		$ 120,000,000	$ 120,000,000.0		$ 9,250,000		$ 22,500,000		$ 13,500,000.0	$ 13,500,000			$ 22,100,000		$ 120,000,000			$ 125,000,000.0	$ 34,600,000.0
Maturity date			Nov. 18, 2015		Sep. 27, 2017			Sep. 27, 2017			Nov. 18, 2017		Jan. 25, 2018		Jan. 25, 2018		Jan. 25, 2018		Jun. 11, 2018			Sep. 30, 2018		Oct. 08, 2018			Oct. 08, 2018			Nov. 18, 2018										Jan. 01, 2018			Jan. 01, 2018
Reference rate (in hundredths)			1-month LIBOR		1-month LIBOR			1-month LIBOR			1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR		1-month LIBOR			1-month LIBOR		1-month LIBOR			1-month LIBOR			1-month LIBOR
Rate at which reference rate is fixed			4.10%		2.20%			2.20%			4.70%		4.94%		4.50%		4.71%					5.20%		5.40%		3.30%	3.30%			5.00%				3.10%
Fair market value liability	8,729,000	15,348,000	0	639,000		61,000	(659,000)		91,000	(994,000)	2,218,000	3,498,000	59,000	0	1,224,000	2,029,000	591,000	1,688,000	1,756,000		0	800,000	1,279,000	2,086,000	3,291,000			0	(8,000)	1,656,000	2,772,000
Remaining ownership by noncontrolling owners purchased (in percent)																																							70.00%
Number of interest rate swaps																																				2
LIBOR rate period fixed (in percent)																																													1.50%		1.45%
Area of real estate property (in square feet)	640,000																																				300,000	299,000	788,000
Frequency of principal payments on existing mortgage																																											quarterly
Quarterly principal payments on existing mortgages																																											625,000
Loan amount	$ 391,000,000																															$ 120,000,000	$ 120,000,000		$ 125,000,000
Maturity date																																									Feb. 01, 2015
LIBOR																																														LIBOR
Fixed base rate of variable interest rate																																										1.70%		1.50%
Basis spread on variable rate (in percent)																																															1.45%	1.50%	2.50%	2.00%	2.30%	3.50%