Discontinued Operations (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012 Property	Dec. 31, 2011
Discontinued Operations and Disposal Groups [Abstract]
Number of industrial properties		2
Number of leased fee properties		2
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations	$ 22.3	$ 12.8	$ 23.3
Basic Earnings Per Share	$ 0.50	$ 0.30	$ 0.55
Diluted Earnings Per Share	$ 0.50	$ 0.30	$ 0.55
Real Estate Leasing
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from the sale of income-producing properties	337.6	8.9	45.5
Real estate leasing revenue	31.6	36.4	36.4
Gain on sale of income-producing properties, net	22.1	4.0	22.5
Real estate leasing operating profit	14.6	17.1	16.3
Total operating profit before taxes	36.7	21.1	38.8
Income tax expense	14.4	8.3	15.5
Income from discontinued operations	$ 22.3	$ 12.8	$ 23.3
Industrial | 2013 Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	4
Retail | 2013 Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	3
Office : | 2013 Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties	2