Goodwill and intangible assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 856,000	$ 265,000
Amortization of Intangible Assets	512,000	$ 79,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	503,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	478,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	444,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	444,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	444,000
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	1,474,000
Polar Technologies, LLC [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill	435,000
Supplier [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 421,000