Derivative Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Effects of derivative instruments
Reclassification adjustment for losses included in termination of derivative instruments and recognized on derivatives in the statements of income				$ (6,410)
Cash Flow Hedging | Designated as Hedging Instruments
Effects of derivative instruments
Amount of Loss Recognized on Derivatives in the Statements of Income	390	11,953	1,149	16,169
Cash Flow Hedging | Loss on debt extinguishment and derivative termination | Designated as Hedging Instruments
Effects of derivative instruments
Reclassification adjustment for losses included in termination of derivative instruments and recognized on derivatives in the statements of income		10,143		10,143
Cash Flow Hedging | Interest rate contracts | Interest expense | Designated as Hedging Instruments
Effects of derivative instruments
Amount of Loss Recognized on Derivatives in the Statements of Income	$ 390	$ 1,810	$ 1,149	$ 6,026