Goodwill and other intangibles Goodwill and other intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 112,739		$ 112,739		$ 72,334
Other Intangible Assets, Net	7,260		7,260		0
Goodwill, Acquired During Period			40,405
Indefinite-lived Intangible Assets Acquired			7,549
Acquired goodwill and intangibles			47,954
Amortization of Intangible Assets	289	$ 0	289	$ 0
Finite-lived Intangible Assets Acquired	6,249		6,249
Indefinite-lived Intangible Assets Acquired	1,300		1,300
Finite-Lived Intangible Assets, Accumulated Amortization	289		289
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	289		289
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1,234		1,234
Finite-Lived Intangible Assets, Amortization Expense, Year Three	1,149		1,149
Finite-Lived Intangible Assets, Amortization Expense, Year Four	869		869
Finite-Lived Intangible Assets, Amortization Expense, Year Five	629		629
Intangible Assets, Gross (Excluding Goodwill)	7,549		7,549
Intangible Assets, Net (Including Goodwill)	119,999		119,999		72,334
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	289		289		$ 0
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 0		$ 0