Goodwill and intangible assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Intangible Assets with determinable lives
Gross Carrying Amount	$ 4,686	$ 4,686
Accumulated Amortization	1,751	1,387
Net	$ 2,935	3,299
Licenses [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	10 years
Gross Carrying Amount	$ 1,000	1,000
Accumulated Amortization	292	217
Net	$ 708	783
Trade Name [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	2 years
Gross Carrying Amount	$ 30	30
Accumulated Amortization	30	30
Net	$ 0	0
Patents [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	5 years
Gross Carrying Amount	$ 386	386
Accumulated Amortization	372	366
Net	14	20
Covenant Not to Compete [Member]
Intangible Assets with determinable lives
Gross Carrying Amount	1,270	1,270
Accumulated Amortization	437	322
Net	$ 833	948
Covenant Not to Compete [Member] | Maximum [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	10 years
Covenant Not to Compete [Member] | Minimum [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	6 years
Customer Relationships [Member]
Intangible Assets with determinable lives
Gross Carrying Amount	$ 2,000	2,000
Accumulated Amortization	620	452
Net	$ 1,380	$ 1,548
Customer Relationships [Member] | Maximum [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	10 years
Customer Relationships [Member] | Minimum [Member]
Intangible Assets with determinable lives
Amortization Period (in years)	3 years