Derivative Instruments and Hedging Activities (Details 1) (Interest rate swaps [Member], Derivatives in Cash Flow Hedging Relationships [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Interest rate swaps [Member] | Derivatives in Cash Flow Hedging Relationships [Member]
Summary of Cash Flow Hedges
Amount of Gain or (Loss) Recognized OCI on Derivatives, net of tax (Effective Portion)	$ (1,484)	$ (2,264)