Capital and Financing Transactions Mortgage (Details) (USD $)			0 Months Ended			6 Months Ended		0 Months Ended			0 Months Ended				0 Months Ended			0 Months Ended		0 Months Ended
	Sep. 30, 2013 sqft	Mar. 25, 2013 Tampa Fund II Assets sqft	Feb. 21, 2013 Phoenix Tower sqft	Sep. 30, 2013 Hayden Ferry Lakeside II sqft	Jun. 28, 2013 Hayden Ferry Lakeside II sqft	Jun. 27, 2013 Hayden Ferry II Original Mortgage Hayden Ferry Lakeside II	Jun. 28, 2013 Hayden Ferry II Original Mortgage Hayden Ferry Lakeside II	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. 28, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II LIBOR	Jun. 28, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II LIBOR Maximum	Jun. 28, 2013 Hayden Ferry II Modified Mortgage Hayden Ferry Lakeside II LIBOR Minimum	Sep. 30, 2013 Mortgages	Feb. 21, 2013 Mortgages Phoenix Tower	Mar. 07, 2013 Mortgages Deerwood Portfolio	Mar. 25, 2013 Mortgages Tampa Fund II Assets	May 31, 2013 Mortgages Corporate Center Four at International Plaza sqft	Aug. 01, 2013 Mortgages Corporate Center Four at International Plaza	Jun. 03, 2013 Mortgages US Airways Building sqft	Jun. 12, 2013 Mortgages Cypress Center and NASCAR Plaza Mortgage	Jun. 12, 2013 Mortgages Cypress Center sqft	Jun. 12, 2013 Mortgages NASCAR Plaza sqft	Sep. 30, 2013 Unsecured Term Loan $120 million LIBOR Maximum	Sep. 30, 2013 Unsecured Term Loan $120 million LIBOR Minimum	Sep. 30, 2013 Wells Fargo Bank Unsecured Term Loan $120 million	Jun. 12, 2013 Wells Fargo Bank Unsecured Term Loan $120 million
Debt Instrument [Line Items]
Modified mortgage loan														$ 722,300,000	$ 80,000,000	$ 84,500,000	$ 40,700,000	$ 22,500,000		$ 13,900,000	$ 55,000,000
Weighted average interest rate (in percent)														5.10%					4.60%		3.60%
Area of real estate property (in square feet)	640,000	788,000	629,000	300,000	299,000													250,000		225,000		286,000	394,000
Interest rate on mortgage (in percent)															3.90%	3.90%				3.00%
Maturity date of debt															March 1, 2023	April 1, 2023
Interest only period of mortgage (in years)			2 years													3 years		24 months
Amortization period of loan principal (in years)															25 years	30 years
Date at which mortgage loan is pre-payable			Mar. 01, 2015													May 01, 2015
Remaining ownership by noncontrolling owners purchased (in percent)		70.00%															70.00%
Proportionate share of mortgage loan																	58,100,000
Modified first mortgage principal balance																		36,000,000
Maturity date									Feb. 01, 2015									Apr. 08, 2019		Dec. 31, 2016
Rate at which reference rate is fixed																		3.30%
Fixed base rate of variable interest rate							1.50%			1.70%
Notional amount																		13,500,000								120,000,000
Loan amount	391,000,000																									120,000,000	120,000,000
Number of first mortgages																					2
Frequency of principal payments on existing mortgage						quarterly
Quarterly principal payments on existing mortgages						$ 625,000
LIBOR											LIBOR
Maturity date						Jan. 01, 2018		Jan. 01, 2018
Basis spread on variable rate (in percent)												3.50%	2.50%											2.00%	1.45%