Goodwill and intangible assets - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Oct. 10, 2017
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 47,803		$ 47,803
Amortization of Intangible Assets	1,474	$ 1,483
Impairment of Intangible Assets, Finite-lived	0		$ 0
Airgas Refrigerants, Inc. [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill				$ 47,000
Amortization of Intangible Assets	$ 1,500	$ 1,500