Goodwill and other intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 112,739	$ 72,334	$ 112,739	$ 72,334
Other Intangible Assets, Net	6,682	0	6,971	0
Goodwill, Acquired During Period	0	0	40,405
Indefinite-lived Intangible Assets Acquired	0	0
Acquired goodwill and intangibles	0	0
Amortization of Intangible Assets	289	0
Finite-lived Intangible Assets Acquired	6,249
Indefinite-lived Intangible Assets Acquired	1,300
Finite-Lived Intangible Assets, Accumulated Amortization	867
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	945
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1,149
Finite-Lived Intangible Assets, Amortization Expense, Year Three	869
Finite-Lived Intangible Assets, Amortization Expense, Year Four	629
Finite-Lived Intangible Assets, Amortization Expense, Year Five	521
Intangible Assets, Gross (Excluding Goodwill)	7,549
Intangible Assets, Net (Including Goodwill)	119,421	$ 72,334	$ 119,710	$ 72,334
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	867
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 0