Derivative Instruments and Hedging Activities - Amounts included in Accumulated Other Comprehensive Loss (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amounts included in accumulated other comprehensive income for derivatives designated as hedging instruments
Unrealized gain (loss) on cash flow hedge included in other comprehensive income	$ (1,241)	$ (932)	$ 320
Interest rate swap [Member] | Cash flow hedge [Member]
Amounts included in accumulated other comprehensive income for derivatives designated as hedging instruments
Unrealized gain (loss) on cash flow hedge included in other comprehensive income	$ (1,241)	$ (932)	$ 320