Derivative Information (Details 2) (USD $)	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011 Interest rate swaps	Jun. 30, 2011 Interest rate swaps	Mar. 22, 2011 Interest rate swaps	Apr. 30, 2007 Designated 5.09 percent interest rate swap	Apr. 30, 2007 Designated 4.97 percent interest rate swap
Derivative Information
Notional value					$ 312,500,000	$ 125,000,000
Fixed rate (as a percent)					5.09%	4.97%
Variable rate basis	LIBOR
Floor rate (as a percent)	1.50%
Deferred losses due to discontinuance of hedge accounting				4,928,000
Deferred losses		4,480,000	4,928,000
Gain on change in fair value of interest rate swap		5,246,000	6,439,000
Non-cash gain on interest rate swap		$ 766,000	$ 1,511,000