Goodwill and intangible assets (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 34,883	$ 34,883
AccumulatedAmortization	6,153	5,432
Net	$ 28,730	29,451
Licenses [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
Gross Carrying Amount	$ 1,000	1,000
AccumulatedAmortization	442	417
Net	$ 558	583
Patents [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	5 years
Gross Carrying Amount	$ 386	386
AccumulatedAmortization	381	380
Net	5	6
Covenant Not to Compete [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	1,270	1,270
AccumulatedAmortization	667	629
Net	$ 603	641
Covenant Not to Compete [Member] | Maximum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
Covenant Not to Compete [Member] | Minimum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	6 years
Customer Relationships [Member]
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 31,660	31,660
AccumulatedAmortization	4,598	3,952
Net	$ 27,062	27,708
Customer Relationships [Member] | Maximum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	12 years
Customer Relationships [Member] | Minimum [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
Above Market Leases [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	13 years
Gross Carrying Amount	$ 567	567
AccumulatedAmortization	65	54
Net	$ 502	$ 513