Derivative Instruments (Details 2) (Cash Flow Hedging [Member], Designated As Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Effects of derivative instruments
Amount of (Gain) Loss Recognized on Derivatives in the Statements of Income	$ (124)	$ 393	$ (249)	$ 759
Interest Rate Contract [Member] | Interest Expense [Member]
Effects of derivative instruments
Amount of (Gain) Loss Recognized on Derivatives in the Statements of Income	$ (124)	$ 393	$ (249)	$ 759