Share-Based Compensation (Details Textuals) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								0 Months Ended	3 Months Ended
	Mar. 31, 2012 Years Share_Based_Incentive_Compensation_Plans	Mar. 31, 2011	Mar. 31, 2012 Time-Based Restricted Stock Units (RSUs) [Member]		Mar. 31, 2012 Market Measure-Based Restricted Stock Units (RSUs) [Member] Years	Mar. 31, 2012 Restricted Stock [Member]	Mar. 31, 2011 Restricted Stock [Member]	Mar. 31, 2012 Stock Options [Member] Years	Mar. 30, 2012 Chief Executive Officer [Member] Restricted Stock Units (RSUs) [Member]	Mar. 31, 2012 Chief Executive Officer [Member] Time-Based Restricted Stock Units (RSUs) [Member]	Mar. 31, 2012 Chief Executive Officer [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Years
Share-Based Compensation (Textuals) [Abstract]
Share-Based Compensation Plans	1
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	703,177
Share based compensation available for grant full value awards subject to full value awards	240,814
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			196,033	[1]		59,938	66,208		206,477	103,239
Type of Restricted Stock Units granted, percentage										50.00%	50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period								5 years		7 years	7 years
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Grants In Period, Grant Date Fair Value										$ 4.8	$ 4.3
Share price	$ 46.61
Vesting Annual Installments											7
Historical volatility, period of computation					14 years
Length of publicly traded options					6 months
Expected life (in years)					7			6.5
Number of shares that were tendered to satisfy minimum statutory tax withholding requirements			4,181	[2]		22,312
Granted, Stock Options	1,550,000
Stock Options, Grants in Period, Weighted Average Exercise Price	$ 42.61
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date								P10Y
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	0
Stock Options, Outstanding, Intrinsic Value	6.2
Share-based compensation programs, total compensation cost	1.5	1.4
Share-based compensation cost capitalized as part of real estate assets	0.2	0.3
Total unrecognized compensation cost related to nonvested incentive awards granted	$ 32.5
Total unrecognized compensation cost weighted-average period, in years	2.8

[1] Includes 103,239 RSUs issued to the Company's Chief Executive Officer, as described above.

[2] We accept the return of RSUs, at the current quoted closing share price of the Company's common stock, to satisfy minimum statutory tax-withholding requirements related to either RSUs that have vested or RSU dividend equivalents in accordance with the terms of the 2006 Plan.