Goodwill and intangible assets - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Oct. 10, 2017
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment loss		$ 0	$ 0	$ 0
Goodwill		47,803	47,803
Amortization of Intangible Assets		2,932	2,973
Impairment of Intangible Assets, Finite-lived		0	$ 0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months		2,900
Finite-Lived Intangible Assets, Amortization Expense, Year Two		2,800
Finite-Lived Intangible Assets, Amortization Expense, Year Three		2,800
Finite-Lived Intangible Assets, Amortization Expense, Year Four		2,800
Finite-Lived Intangible Assets, Amortization Expense, Year Five		2,800
Finite-Lived Intangible Assets, Amortization Expense, after Year Five		$ 11,900
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