Derivative Instruments (Narrative) (Details) In Millions, unless otherwise specified	0 Months Ended		12 Months Ended												3 Months Ended	12 Months Ended
	Jan. 05, 2012 swap_agreements	Feb. 07, 2011 swap_agreements	Dec. 31, 2011 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 Cash Flow Hedging [Member] USD ($)	Sep. 06, 2013 Interest Rate Swap [Member]	Jan. 05, 2012 Interest Rate Swap [Member] USD ($)	Dec. 31, 2013 Interest Rate Risk [Member] USD ($)	Dec. 31, 2013 Cross Currency Swaps [Member] USD ($)	Dec. 31, 2013 Cross Currency Swaps [Member] CAD	Dec. 31, 2013 Cross Currency Swaps [Member] Cash Flow Hedging [Member] CAD	Jun. 19, 2013 Cross Currency Swaps [Member] Cash Flow Hedging [Member] USD ($)	Jun. 19, 2013 Cross Currency Swaps [Member] Cash Flow Hedging [Member] CAD	Mar. 29, 2011 Currency Forward Agreements [Member] Net Investment Hedging [Member] USD ($)	Dec. 31, 2013 Currency Forward Agreements [Member] Net Investment Hedging [Member] USD ($) properties	Dec. 31, 2013 Currency Forward Agreements [Member] Net Investment Hedging [Member] CAD properties	Jun. 19, 2013 Currency Forward Agreements [Member] Net Investment Hedging [Member] USD ($)	Jun. 19, 2013 Currency Forward Agreements [Member] Net Investment Hedging [Member] CAD	Feb. 03, 2011 Currency Forward Agreements [Member] Net Investment Hedging [Member] USD ($)	Feb. 03, 2011 Currency Forward Agreements [Member] Net Investment Hedging [Member] CAD
credit risk related contingent features default on debt amount				$ 25.0
Derivative Liability, Fair Value, Gross Liability				4.5	8.1
Derivative, Fair Value, Net				1.6
Derivative Liability					8.0
Derivative Asset, Fair Value, Gross Asset				6.1	0.1
Number of terminated interest rate swap agreements		6
Derivative, Fixed Interest Rate							2.38%	2.51%
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net									1.7
Interest rate swap reclassified into earning as expenses			4.6
Number of entered into interest rate swap agreements	3
Amount of hedged term loan								240.0
Net exchange rate, CAD to US dollar											1.05			1.05			1.04	1.06
Number of Canadian properties exposed to foreign currency exchange risk																4	4
Cash flows on the properties												13.0		13.5
Estimated amount to be reclassified from accumulated other comprehensive income to other expense in the next twelve months						0.2
Derivative, Notional Amount			87.7					240.0		71.5	76.0		98.1	100.0		96.1	100.0	94.3	100.0	201.5	200.0
Loss on settlement of derivative contract conjunction with sale of property															$ 4.3