Acquisitions, Dispositions and Mortgage Repayments (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Business Acquisition [Line Items]
Prepaid ground lease	$ 0.7		$ 12.8
Intangibles
At-market lease intangibles	6.2		10.5
Above-market lease intangibles			0.3
Below-market lease intangibles			(0.1)
Total intangibles	6.2		10.7
Accounts receivable and other assets acquired			0.3
Mortgage notes payable assumed, including fair value adjustment	(5.2)		(54.4)
Mortgage notes payable repayments	(9.9)
Accounts payable, accrued liabilities and other liabilities assumed	(0.9)		(0.5)
Prorated rent, net of expenses paid	0.3		0.6
Total cash consideration	89.8	[1]	114.5	[2]
Estimated useful life, buildings, minimum	20 years		25 years
Estimated useful life, buildings, maximum	38 years		33 years
Estimated useful life, prepaid ground lease	54 years
Estimated useful life, prepaid ground lease, minimum			94 years 2 months 12 days
Estimated useful life, prepaid ground lease, maximum			94 years 6 months
Estimated useful life, intangibles at-market lease intangibles, minimum	4 years 10 months 24 days		2 years
Estimated useful life, intangibles at market lease intangibles, maximum	19 years 3 months 18 days		5 years
Estimated useful life, intangibles above-market lease intangibles, minimum			10 months 24 days
Estimated useful life, intangibles above-market lease intangibles, maximum			4 years 8 months 12 days
Estimated useful life, intangibles below-market lease intangibles, minimum			2 years 8 months 12 days
Estimated useful life, intangibles below-market lease intangibles, maximum			6 years 3 months 18 days
Acquisition and closing costs expensed	0.5
Building [Member]
Business Acquisition [Line Items]
Purchase price allocation, property	85.1		139.5
Land [Member]
Business Acquisition [Line Items]
Purchase price allocation, property	$ 13.5		$ 5.5

[1] Total cash consideration includes receivables acquired and liabilities assumed in the acquisition as well as rental prorations and expense disbursements

[2] Total cash consideration includes receivables acquired and liabilities assumed in the acquisition as well as rental prorations and expense disbursements.