Banking Facilities and Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Banking facilities and debt
Amendment fee	$ 100,000
Cash flow leverage ratio	3.25
Summary of outstanding debt
Debt	26,667,000	32,917,000
Less current installments	5,000,000	6,250,000
Debt, excluding current installments	21,667,000	26,667,000
Principal amounts payable on the long-term debt outstanding
2013	5,000,000
2014	5,000,000
2015	16,667,000
Total	21,667,000	26,667,000
Interest rate swaps
Interest rate hedges
Interest rate swap liabilities	2,600,000	3,500,000
Interest rate swap liabilities included in accrued expenses	1,100,000	1,300,000
Interest rate swap liabilities included in other liabilities	1,500,000	2,200,000
Quarterly settlement payment pursuant to hedges	1,300,000	1,600,000
LIBOR
Banking facilities and debt
Interest rate basis	LIBOR
Lender's prime rate
Banking facilities and debt
Interest rate basis	Lender's Prime Rate
Prior to the Amendment
Banking facilities and debt
Cash flow leverage ratio	3.50
Minimum | LIBOR
Banking facilities and debt
Interest rate margin (as a percent)	1.75%
Minimum | Lender's prime rate
Banking facilities and debt
Interest rate margin (as a percent)	0.00%
Minimum | Prior to the Amendment | LIBOR
Banking facilities and debt
Interest rate margin (as a percent)	1.125%
Minimum | Prior to the Amendment | Lender's prime rate
Banking facilities and debt
Interest rate margin (as a percent)	(0.50%)
Maximum
Banking facilities and debt
Pro forma Cash Flow Leverage Ratio to be maintained to purchase, redeem or otherwise acquire shares of common stock	3.00
Maximum | LIBOR
Banking facilities and debt
Interest rate margin (as a percent)	2.75%
Maximum | Lender's prime rate
Banking facilities and debt
Interest rate margin (as a percent)	1.00%
Maximum | Prior to the Amendment | LIBOR
Banking facilities and debt
Interest rate margin (as a percent)	2.125%
Maximum | Prior to the Amendment | Lender's prime rate
Banking facilities and debt
Interest rate margin (as a percent)	0.375%
Term Loan
Banking facilities and debt
Term	10 years
Maximum borrowing capacity	40,000,000
Quarterly principal payments	833,000
Final principal payment	10,000,000
Summary of outstanding debt
Debt	16,667,000	20,834,000
Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)	4.695%
Interest rate during the period (as a percent)	6.445%
Term Loan | Prior to the Amendment | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	5.82%
Draw Term Loan
Banking facilities and debt
Term	10 years
Maximum borrowing capacity	20,000,000
Quarterly principal payments	417,000
Final principal payment	6,700,000
Summary of outstanding debt
Debt	10,000,000	12,083,000
75% the outstanding balance of the Draw Term Loan | Interest rate swaps
Interest rate hedges
Percentage of outstanding balance of debt hedged	75.00%
75% the outstanding balance of the Draw Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)	4.875%
Interest rate during the period (as a percent)	6.625%
75% the outstanding balance of the Draw Term Loan | Prior to the Amendment | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	6.00%
25% the outstanding balance of the Draw Term Loan | Interest rate swaps
Interest rate hedges
Percentage of outstanding balance of debt hedged	25.00%
25% the outstanding balance of the Draw Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)	5.50%
Interest rate during the period (as a percent)	7.25%
25% the outstanding balance of the Draw Term Loan | Prior to the Amendment | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	6.625%
Revolving Facility
Banking facilities and debt
Maximum borrowing capacity	30,000,000
Letters of credit outstanding	$ 637,000
Revolving Facility | Minimum
Banking facilities and debt
Commitment fee (as a percent)	0.25%
Revolving Facility | Minimum | Prior to the Amendment
Banking facilities and debt
Commitment fee (as a percent)	0.20%
Revolving Facility | Maximum
Banking facilities and debt
Commitment fee (as a percent)	0.40%
Revolving Facility | Maximum | Prior to the Amendment
Banking facilities and debt
Commitment fee (as a percent)	0.35%