Intangibles (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Y	Dec. 31, 2011	Dec. 31, 2010
Acquired Finite-Lived Intangible Assets [Line Items]
Future Amortization Expense, Period	5 years
Leases, Acquired-in-Place [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization period (in years)	7
Gross carrying amount	$ 35.3	$ 25.3
Accumulated amortization	11.8	10.8
Aggregate net amortization net expense	3.6	2.5	2.5
Anticipated amortization [Abstract]
Anticipated amortization expense, 2012	4.3
Anticipated amortization expense, 2013	4.0
Anticipated amortization expense, 2014	3.8
Anticipated amortization expense, 2015	3.6
Anticipated amortization expense, 2016	$ 3.4