Banking Facilities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Summary of outstanding debt
Debt	$ 29,167,000		$ 29,167,000		$ 32,917,000
Less current installments	6,250,000		6,250,000		6,250,000
Debt, excluding current installments	22,917,000		22,917,000		26,667,000
Interest rate swaps
Interest rate hedges
Interest rate swap liabilities	3,000,000		3,000,000		3,500,000
Interest rate swap liabilities included in accrued expenses	1,200,000		1,200,000		1,300,000
Interest rate swap liabilities included in other liabilities	1,800,000		1,800,000		2,200,000
Quarterly settlement payment pursuant to hedges	321,000	399,000	1,000,000	1,200,000
LIBOR
Banking facilities
Interest rate basis			LIBOR
Lender's prime rate
Banking facilities
Interest rate basis			Lender's Prime Rate
Minimum | LIBOR
Banking facilities
Interest rate margin (as a percent)	1.75%		1.75%
Minimum | Lender's prime rate
Banking facilities
Interest rate margin (as a percent)	0.00%		0.00%
Maximum | LIBOR
Banking facilities
Interest rate margin (as a percent)	2.75%		2.75%
Maximum | Lender's prime rate
Banking facilities
Interest rate margin (as a percent)	1.00%		1.00%
Term Loan
Banking facilities
Term			10 years
Maximum borrowing capacity	40,000,000		40,000,000
Quarterly principal payments			833,000
Amortization period of debt instrument			12 years
Final principal payment			10,000,000
Summary of outstanding debt
Debt	18,334,000		18,334,000		20,834,000
Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)			4.695%
Term Loan | Minimum | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	6.445%		6.445%
Draw Term Loan
Banking facilities
Term			10 years
Maximum borrowing capacity	20,000,000		20,000,000
Quarterly principal payments			417,000
Amortization period of debt instrument			12 years
Final principal payment			6,700,000
Summary of outstanding debt
Debt	10,833,000		10,833,000		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%		75.00%
75% the outstanding balance of the Draw Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)			4.875%
75% the outstanding balance of the Draw Term Loan | Minimum | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	6.625%		6.625%
25% the outstanding balance of the Draw Term Loan | Interest rate swaps
Interest rate hedges
Percentage of outstanding balance of debt hedged	25.00%		25.00%
25% the outstanding balance of the Draw Term Loan | LIBOR | Interest rate swaps
Interest rate hedges
LIBOR (as a percent)			5.50%
25% the outstanding balance of the Draw Term Loan | Minimum | LIBOR | Interest rate swaps
Interest rate hedges
Interest rate during the period (as a percent)	7.25%		7.25%
Revolving Facility
Banking facilities
Maximum borrowing capacity	30,000,000		30,000,000
Letters of credit outstanding	$ 343,000		$ 343,000		$ 322,000
Revolving Facility | Minimum
Banking facilities
Commitment fee (as a percent)			0.25%
Revolving Facility | Maximum
Banking facilities
Commitment fee (as a percent)			0.40%