Derivative Financial Instruments (Details 2) (Interest Rate Swaps, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Term April 2013 to December 2013
Derivative Financial Instruments
Weighted Average Notional Amount	$ 227,103
Weighted Average Fixed Rate (as a percent)	2.06%
Floating Rate	6-month LIBOR
Term January 2014 to December 2014
Derivative Financial Instruments
Weighted Average Notional Amount	133,434
Weighted Average Fixed Rate (as a percent)	1.99%
Floating Rate	6-month LIBOR
Term January 2015 to December 2015
Derivative Financial Instruments
Weighted Average Notional Amount	45,319
Weighted Average Fixed Rate (as a percent)	2.03%
Floating Rate	6-month LIBOR
Term January 2016 to June 2016
Derivative Financial Instruments
Weighted Average Notional Amount	$ 12,500
Weighted Average Fixed Rate (as a percent)	2.27%
Floating Rate	6-month LIBOR