Federal Income Tax Considerations (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Income Tax Note [Line Items]
Required distribution percentage to maintain REIT status	90.00%
Fixed assets book value in excess of (less than) tax basis	$ (7.0)	$ (37.0)
Future dividends designated in dividends paid deduction		3.8
Current tax obligation	$ 1.9	$ 1.5