Reportable Segments Table (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Reimbursed Expenses	$ (686,000)	$ (783,000)	$ (2,514,000)	$ (2,703,000)
Dividends, Preferred Stock	0	0	0	2,955,000
Net income available to common stockholders	53,620,000	19,322,000	68,774,000	22,299,000
Office Segment [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	59,328,000	52,691,000	175,331,000	149,110,000
Residential lot and other sales, net of cost of sales	0	0	0	0
Fee income, Net of Reimbursed Expenses	0	0	0	0
Other Income	0	0	0	0
General and Administrative Expense	0	0	0	0
Reimbursed Expenses	0	0	0	0
Interest Expense Including Discontinued Operations	0	0	0	0
Other nonoperating expense, including discontinued operations	0	0	0	0
Dividends, Preferred Stock		0		0
Funds from Operations Available to Common Stockholders	59,328,000	52,691,000	175,331,000	149,110,000
Retail Segment [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	1,221,000	0	3,813,000
Residential lot and other sales, net of cost of sales	0	0	0	0
Fee income, Net of Reimbursed Expenses	0	0	0	0
Other Income	0	0	0	0
General and Administrative Expense	0	0	0	0
Reimbursed Expenses	0	0	0	0
Interest Expense Including Discontinued Operations	0	0	0	0
Other nonoperating expense, including discontinued operations	0	0	0	0
Dividends, Preferred Stock		0		0
Funds from Operations Available to Common Stockholders	0	1,221,000	0	3,813,000
Land [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Residential lot and other sales, net of cost of sales	3,016,000	82,000	3,502,000	1,573,000
Fee income, Net of Reimbursed Expenses	0	0	0	0
Other Income	0	0	0	0
General and Administrative Expense	0	0	0	0
Reimbursed Expenses	0	0	0	0
Interest Expense Including Discontinued Operations	0	0	0	0
Other nonoperating expense, including discontinued operations	0	0	0	0
Dividends, Preferred Stock		0		0
Funds from Operations Available to Common Stockholders	3,016,000	82,000	3,502,000	1,573,000
All Other Segments [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	1,488,000	1,200,000	4,312,000	3,496,000
Residential lot and other sales, net of cost of sales	0	0	0	42,000
Fee income, Net of Reimbursed Expenses	1,686,000	1,802,000	5,206,000	6,165,000
Other Income	845,000	399,000	1,490,000	4,563,000
General and Administrative Expense	(2,971,000)	(5,021,000)	(12,502,000)	(16,472,000)
Reimbursed Expenses	(686,000)	(783,000)	(2,514,000)	(2,703,000)
Interest Expense Including Discontinued Operations	(9,518,000)	(8,660,000)	(28,712,000)	(26,485,000)
Other nonoperating expense, including discontinued operations	(721,000)	(1,255,000)	(2,473,000)	(2,974,000)
Dividends, Preferred Stock		0		6,485,000
Funds from Operations Available to Common Stockholders	(9,877,000)	(12,318,000)	(35,193,000)	(40,853,000)
Total Segment [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	60,816,000	55,112,000	179,643,000	156,419,000	$ 156,419,000	$ 179,643,000
Residential lot and other sales, net of cost of sales	3,016,000	82,000	3,502,000	1,615,000	1,615,000
Fee income, Net of Reimbursed Expenses	1,686,000	1,802,000	5,206,000	6,165,000	6,165,000
Other Income	845,000	399,000	1,490,000	4,563,000	$ 4,563,000
General and Administrative Expense	(2,971,000)	(5,021,000)	(12,502,000)	(16,472,000)
Reimbursed Expenses	(686,000)	(783,000)	(2,514,000)	(2,703,000)
Interest Expense Including Discontinued Operations	(9,518,000)	(8,660,000)	(28,712,000)	(26,485,000)
Other nonoperating expense, including discontinued operations	(721,000)	(1,255,000)	(2,473,000)	(2,974,000)
Dividends, Preferred Stock		0		6,485,000
Funds from Operations Available to Common Stockholders	52,467,000	41,676,000	143,640,000	113,643,000
Real estate depreciation and amortization, including Company's share of joint ventures	(35,014,000)	(35,347,000)	(110,759,000)	(110,319,000)
Gain on sale of depreciated investment properties, including Company's share of joint ventures	36,167,000	12,993,000	35,893,000	18,975,000
Net income available to common stockholders	$ 53,620,000	$ 19,322,000	$ 68,774,000	$ 22,299,000