Fair Value Measurements (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended
	Apr. 30, 2012 Y	Mar. 31, 2012 Y
Trading Activity, Gains and Losses, Net [Line Items]
Derivative fixed interest rate	3.21%	3.06%
Swap contract notional amount fixed rate of interest and variable LIBOR	$ 250,000,000	$ 200,000,000
Derivative Fixed Interest Rate Term	10	10
Roll Adjustment Swap Contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Asset value attributable to roll adjustment swaps		$ 213,000