Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			12 Months Ended			1 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2006	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 Minimum [Member]	Jul. 31, 2011 Outdated Unsecured Short Term Revolving Credit Facility [Member]	Jul. 31, 2011 Amended And Restated Unsecured Short Term Revolving Credit Facility [Member]	Dec. 31, 2012 Minimum Credit Spread On LIBOR Or CDOR Borrowings [Member]	Dec. 31, 2012 Maximum Credit Spread On LIBOR Or CDOR Borrowings [Member]	Dec. 31, 2012 Maximum Credit Spread On Prime Rate Borrowings [Member]
Line of Credit Facility [Line Items]
Borrowing capacity						$ 200	$ 300
Credit Facility maturity date							Jul. 25, 2016
Outstanding Credit Facility balance	212.0	243.0
Credit Facility weighted average interest rates on outstanding balance	1.30%	1.70%
Credit spread during period								0.875%	1.25%	0.25%
Reduction of Credit Facility Availability	1.0	1.0
Commitment fees				0.30%	0.15%
Consolidated leverage ratio under credit facility, maximum	3
Face value of mortgage at inception			6.5
Fair value of mortgage at inception			7.5
Mortgage stated interest rate			9.875%
Equal monthly installments due on mortgage	$ 0.1
Mortgage maturity date	May 01, 2015