Financial Derivative Instruments (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Derivative, Fair Value [Line Items]
Fair value of derivatives, net liability	$ 2,764,000	$ 2,469,000
Interest Rate Swap Agreement [Member]
Interest-Rate Swap Agreement [Line Items]
Coverage Amount	72,000,000
Interest Rate Swap September 2014 [Member] | Interest Rate Swap Agreement [Member]
Interest-Rate Swap Agreement [Line Items]
Coverage Amount	24,000,000
Variable Interest Rate (in hundredths)	1.66%
Interest Rate Swap March 2015 [Member] | Interest Rate Swap Agreement [Member]
Interest-Rate Swap Agreement [Line Items]
Coverage Amount	24,000,000
Variable Interest Rate (in hundredths)	1.91%
Interest Rate Swap September 2015 [Member] | Interest Rate Swap Agreement [Member]
Interest-Rate Swap Agreement [Line Items]
Coverage Amount	$ 24,000,000
Variable Interest Rate (in hundredths)	2.14%