Acquisitions and Dispositions (Details 5) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues
Property operating	$ 60,948,000		$ 53,320,000	$ 119,913,000	$ 105,141,000
Single-tenant net lease	12,833,000		13,459,000	25,092,000	27,503,000
Straight-line rent	1,542,000		1,076,000	3,449,000	2,364,000
Other operating	1,374,000		2,047,000	3,146,000	4,345,000
Revenues	78,736,000		71,727,000	155,931,000	142,827,000
Expenses
Property operating	29,457,000		27,773,000	58,039,000	55,210,000
General and administrative	4,519,000		5,157,000	9,782,000	10,938,000
Depreciation	21,311,000		18,487,000	42,333,000	36,756,000
Amortization	(2,540,000)		(1,778,000)	(5,077,000)	(3,555,000)
Bad debt, net	149,000		93,000	109,000	271,000
Total Expenses	57,976,000		53,288,000	115,340,000	106,730,000
Other Income (Expense)
Interest and other income, net	203,000		196,000	508,000	418,000
Total other income (expense)	(18,327,000)		(17,147,000)	(36,401,000)	(41,185,000)
Discontinued Operations
Income from discontinued operations	659,000		719,000	2,777,000	1,448,000
Impairments	(167,000)		0	(4,336,000)	(147,000)
Gain on sales of real estate properties	3,000	3,400,000	0	3,431,000	36,000
INCOME FROM DISCONTINUED OPERATIONS	495,000		719,000	1,872,000	1,337,000
Income (Loss) from Discontinued Operations per Common Share - Basic	$ 0.01		$ 0.01	$ 0.03	$ 0.02
Income (Loss) from Discontinued Operations per Common Share - Diluted	$ 0.01		$ 0.01	$ 0.03	$ 0.02
Long Lived Assets Held-for-sale, Impairment Charge	3,800,000			3,800,000
Discontinued Operations [Member]
Revenues
Property operating	269,000		665,000	910,000	1,436,000
Single-tenant net lease	766,000		1,643,000	3,391,000	3,287,000
Straight-line rent	3,000		33,000	(4,000)	31,000
Other operating	2,000		6,000	9,000	13,000
Revenues	1,040,000		2,347,000	4,306,000	4,767,000
Expenses
Property operating	305,000		1,006,000	1,111,000	2,067,000
General and administrative	1,000		3,000	4,000	5,000
Depreciation	121,000		633,000	487,000	1,259,000
Amortization	0		8,000	0	16,000
Bad debt, net	1,000		0	(1,000)	16,000
Total Expenses	428,000		1,634,000	1,601,000	3,331,000
Other Income (Expense)
Interest and other income, net	47,000		6,000	72,000	12,000
Total other income (expense)	47,000		6,000	72,000	12,000
Discontinued Operations
Income from discontinued operations	659,000		719,000	2,777,000	1,448,000
Impairments	(167,000)		0	(4,336,000)	(147,000)
Gain on sales of real estate properties	3,000		0	3,431,000	36,000
INCOME FROM DISCONTINUED OPERATIONS	$ 495,000		$ 719,000	$ 1,872,000	$ 1,337,000
Income (Loss) from Discontinued Operations per Common Share - Basic	$ 0.01		$ 0.01	$ 0.03	$ 0.02
Income (Loss) from Discontinued Operations per Common Share - Diluted	$ 0.01		$ 0.01	$ 0.03	$ 0.02