Derivative Instruments (Details) (USD $)	9 Months Ended			3 Months Ended
	Sep. 30, 2011 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2005, maturity in July 2020 contract	Sep. 30, 2011 Interest rate swap, variable rate, secured debt Interest rate swap, entered in November 2008, maturity in October 2016	Sep. 30, 2011 Interest rate swap, variable rate, secured debt Interest rate swap, entered in July 2009, maturity in July 2013	Mar. 31, 2011 Interest rate swap, entered in August 2009, maturity in August 2011
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 (as a percent)		1.50%	3.65%
Notional Amount	$ 45,600,000	$ 27,800,000	$ 14,000,000
Interest-swap liabilities	(7,133,000)	(4,219,000)	(496,000)
Number of interest-rate swap contracts	3
Reclassification of unrealized gains into other income (expense)				1,000,000
Proceeds from settlement of interest rate swap contract				1,000,000
Effects of Change in Interest Rates
+50 Basis Points	1,683,000	659,000	119,000
-50 Basis Points	(2,019,000)	(654,000)	(124,000)
+100 Basis Points	3,535,000	1,315,000	241,000
-100 Basis Points	$ (3,870,000)	$ (1,310,000)	$ (246,000)