Goodwill and intangible assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 10, 2017
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 49,464	$ 856		$ 48,609
Amortization of Intangible Assets	1,107	$ 488	$ 512
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	3,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	3,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	3,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	3,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	3,000
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	17,400
Polar Technologies, LLC [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill				400
Supplier [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill				$ 400
Airgas Refrigerants, Inc. [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 48,600