Goodwill and intangible assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Indefinite-lived Intangible Assets [Line Items]
GrossCarryingAmount	$ 4,686	$ 4,687
AccumulatedAmortization	1,387	900
Net	$ 3,299	3,787
License Agreement Terms [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
GrossCarryingAmount	$ 1,000	1,000
AccumulatedAmortization	217	117
Net	$ 783	883
Trade Names [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	2 years
GrossCarryingAmount	$ 30	30
AccumulatedAmortization	30	24
Net	$ 0	6
Patents [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	5 years
GrossCarryingAmount	$ 386	387
AccumulatedAmortization	366	352
Net	20	35
Noncompete Agreements [Member]
Indefinite-lived Intangible Assets [Line Items]
GrossCarryingAmount	1,270	1,270
AccumulatedAmortization	322	171
Net	$ 948	1,099
Noncompete Agreements [Member] | Maximum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
Noncompete Agreements [Member] | Minimum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	6 years
Customer Relationships [Member]
Indefinite-lived Intangible Assets [Line Items]
GrossCarryingAmount	$ 2,000	2,000
AccumulatedAmortization	452	236
Net	$ 1,548	$ 1,764
Customer Relationships [Member] | Maximum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
Customer Relationships [Member] | Minimum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	3 years