Derivative Financial Instruments (Details) (USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2011 Interest rate swap, entered in August 2009, maturity in August 2011	Jun. 30, 2012 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2005, maturity in July 2020 item	Jun. 30, 2012 Interest rate swap, variable rate, secured debt Interest rate swap, entered in November 2008, maturity in October 2016	Jun. 30, 2012 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2009, maturity in July 2013
Derivative
Fixed Rate (as a percent)		3.82%	5.95%	6.13%
Floating Rate Index		BMA Swap Index	1 Month LIBOR	1 Month LIBOR
Floating Rate Index, percentage			1.50%	3.65%
Notional Amount		$ 45,600,000	$ 27,300,000	$ 13,800,000
Fair value of hedge, liabilities		(8,445,000)	(4,159,000)	(299,000)
Number of interest-rate swap contracts		3
Reclassification of unrealized gains into other income	1,000,000
Proceeds from settlement of interest rate swap contract	1,000,000
Effects of Change in Interest Rates
+50 Basis Points		1,610,000	556,000	66,000
-50 Basis Points		(1,840,000)	(561,000)	(73,000)
+100 Basis Points		3,335,000	1,114,000	136,000
-100 Basis Points		$ (3,565,000)	$ (1,119,000)	$ (142,000)