Summary of Significant Accounting Policies (Details 2) (USD $)									9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Total at the end of the period	Dec. 31, 2012 Total at the end of the period	Sep. 30, 2013 Level 2	Dec. 31, 2012 Level 2	Sep. 30, 2013 Level 3	Dec. 31, 2012 Level 3	Sep. 30, 2013 Level 3 Maximum	Sep. 30, 2013 Level 3 Minimum	Sep. 30, 2013 Interest Rate Cap Agreement item	Dec. 31, 2012 Interest Rate Cap Agreement item	Sep. 30, 2013 Interest Rate Swap Agreement item	Dec. 31, 2012 Interest Rate Swap Agreement item
Fair value of assets and liabilities measured at fair value on a recurring and non-recurring basis
Number of derivative agreements											2	2
Number of derivative agreements													1	1
Percentage of debt having fixed interest rates	70.80%	69.60%
Carrying value of secured debt	$ 1,410,357,000	$ 1,363,389,000
Weighted average cost of debt (as a percent)									5.50%	5.00%
Fair value of debt							1,400,000,000	1,300,000,000
Assets:
Interest rate cap derivative agreements	49,000	48,000	49,000	48,000	49,000	48,000					49,000	48,000
Life insurance policy			1,376,000	1,494,000	1,376,000	1,494,000
Total assets			1,425,000	1,542,000	1,425,000	1,542,000
Liabilities:
Interest rate swap derivative agreements			1,196,000	1,636,000	1,196,000	1,636,000							1,200,000	1,600,000
Retirement benefit agreement			1,376,000	1,494,000	1,376,000	1,494,000
Total liabilities			2,572,000	3,130,000	2,572,000	3,130,000
Accounts Receivable
Allowance for doubtful accounts	$ 200,000	$ 200,000