Goodwill and intangible assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets [Line Items]
GrossCarryingAmount	$ 34,913	$ 4,686
AccumulatedAmortization	2,494	1,387
Net	$ 32,419	3,299
Licenses [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	10 years
GrossCarryingAmount	$ 1,000	1,000
AccumulatedAmortization	317	217
Net	$ 683	783
Patents [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	5 years
GrossCarryingAmount	$ 386	386
AccumulatedAmortization	374	366
Net	12	20
Covenant Not to Compete [Member]
Indefinite-lived Intangible Assets [Line Items]
GrossCarryingAmount	1,270	1,270
AccumulatedAmortization	475	322
Net	$ 795	948
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]
GrossCarryingAmount	$ 31,660	2,000
AccumulatedAmortization	1,288	452
Net	$ 30,372	1,548
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)	3 years
Above Market Leases [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	13 years
GrossCarryingAmount	$ 567	0
AccumulatedAmortization	10	0
Net	$ 557	0
Trade Names [Member]
Indefinite-lived Intangible Assets [Line Items]
Amortization Period(in years)	2 years
GrossCarryingAmount	$ 30	30
AccumulatedAmortization	30	30
Net	$ 0	$ 0