Short-term and long-term debt - Additional Information (Detail)		3 Months Ended	12 Months Ended
	Jul. 01, 2015	Sep. 30, 2013	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Feb. 15, 2013 USD ($)	Jun. 01, 2012 USD ($)
Maximum borrowing under PNC facility					$ 40,000,000
PNC Facility effective rate of interest			3.75%
Capital leased assets gross			$ 296,000
Interest rate description under PNC facility			Interest charges with respect to loans are computed on the actual principal amount of loans outstanding during the month at a rate per annum equal to (A) with respect to Domestic Rate Loans (as defined in the PNC Facility), the sum of the Alternate Base Rate (as defined in the PNC Facility) plus one half of one percent (.50%) and (B) with respect to Eurodollar Rate Loans, the sum of the Eurodollar Rate plus two and one quarter of one percent (2.25%).
Principal balance of this mortgage note			$ 260,000	$ 437,000
Deferred Finance Costs, Net					38,000
Long-term Line of Credit			24,227,000
Line of Credit Facility, Current Borrowing Capacity			$ 15,773,000
Debt Instrument, Maturity Date			Jun. 30, 2018
Revolving Credit Facility
Maximum borrowing under PNC facility					36,000,000
Revolving Credit Facility | Base Rate
Debt instrument, description of variable rate basis			Alternate Base Rate (as defined in the PNC Facility) plus one half of one percent
Debt Instrument, Basis Spread on Variable Rate	0.50%		0.50%
Revolving Credit Facility | Eurodollar
Debt instrument, description of variable rate basis			Eurodollar Rate plus two and one quarter of one percent
Minimum
Fixed charge coverage ratio		1.00	1.00
Maximum
Fixed charge coverage ratio		1.10	1.10
Mortgage Note
Maximum borrowing under PNC facility						$ 855,000
PNC Facility effective rate of interest						4.00%
Line of Credit Facility, Expiration Date			Jun. 01, 2017
Vehicle and Equipment Loans | Minimum
PNC Facility effective rate of interest			2.90%
Vehicle and Equipment Loans | Maximum
PNC Facility effective rate of interest			6.70%
Term Loan
Maximum borrowing under PNC facility					$ 4,000,000
Term Loan | Base Rate
Debt instrument, description of variable rate basis			Base Rate plus one half of one percent
Term Loan | Revolving Credit Facility | Base Rate
Debt Instrument, Basis Spread on Variable Rate			0.50%
Eurodollar Rates | Revolving Credit Facility
Debt Instrument, Basis Spread on Variable Rate	2.25%		2.25%
Eurodollar Rates | Term Loan
Debt instrument, description of variable rate basis			Eurodollar Rate plus two and one quarter of one percent
Debt Instrument, Basis Spread on Variable Rate			2.25%