Goodwill and Other Intangibles and Mortgage Servicing Rights - Goodwill and other intangibles (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 151,198	$ 151,198	$ 107,366
Other intangibles	13,776	14,769
Goodwill and other intangibles, net	164,974	165,967
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Other intangibles	10,031	10,897
Customer list intangibles:
Finite-Lived Intangible Assets [Line Items]
Other intangibles	$ 3,745	$ 3,872