Derivative Instruments (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments (Textual) [Abstract]
Open forward foreign currency exchange contract not designated as a hedge	$ 16,258,000	$ 26,627,000
Open forward foreign currency exchange contract designated as a cash flow hedge	1,197,000	5,266,000
Open interest rate contracts designated as a cash flow hedge	$ 2,969,000	$ 3,693,624