Goodwill and other intangibles - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Increase in goodwill		$ 17,504
Other intangibles, gross carrying amount	$ 35,000	35,000
Accumulated amortization of other intangibles	30,400	25,300
Amortization expense of other intangibles	4,200	4,600
Impairment expense of other intangible assets	900
Future amortization expense
Expected amortization expense in 2020	2,300
Expected amortization expense in 2021	900
Expected amortization expense in 2022	400
Expected amortization expense in 2023	200
Expected amortization expense in 2024	$ 200
Employment and Non-compete Agreements
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangibles acquired		$ 4,500
Employment and Non-compete Agreements | Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization period		1 year
Employment and Non-compete Agreements | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization period		3 years
Title
Acquired Finite-Lived Intangible Assets [Line Items]
Increase in goodwill		$ 17,504