Accounting Policies Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deferred financing costs amortization	$ 2,300,000	$ 2,400,000	$ 3,100,000
Deferred leasing costs amortization	4,600,000	4,400,000	4,000,000
Deferred leasing incentives amortization	700,000	200,000	100,000
Real estate depreciation	71,200,000	64,800,000	62,300,000
Capitalized interest	700,000	900,000	1,400,000
Accumulated other comprehensive income (loss)	0	(1,469,000)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(1,469,000)	(288,000)	(578,000)
Gross Carrying Value Deferred Leasing Incentives [Member]
Incentive to Lessee, Gross Carrying Value	4,800,000	2,600,000
Accumulated Amortization Deferred Leasing Incentives [Member]
Incentive to Lessee, Accumulated Amortization	1,000,000	400,000
Net Deferred Leasing Incentives [Member]
Incentive to Lessee	$ 3,800,000	$ 2,200,000