Goodwill and intangible assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Oct. 10, 2017
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 47,803	$ 47,803		$ 47,803
Amortization of Intangible Assets		2,216	$ 2,225
Impairment of Intangible Assets, Finite-lived		0		$ 0
Nashville and Puerto Rico
Indefinite-lived Intangible Assets [Line Items]
Impairment of Intangible Assets, Finite-lived	$ 500
Airgas Refrigerants, Inc. [Member]
Indefinite-lived Intangible Assets [Line Items]
Goodwill					$ 47,000
Amortization of Intangible Assets		$ 2,200	$ 2,200