Loans and Allowance for Loan Losses - Aging Analysis Of The Recorded Investment In Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Aging analysis of loan portfolio
Past due loans	$ 4,253	$ 4,175
Current loans	1,370,407	937,621
Loans and Leases Receivable, Net of Deferred Income, Total	1,374,660	941,796
30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	59	184
60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	1,054	2,104
Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	3,140	1,887
Mortgage warehouse lines of credit
Aging analysis of loan portfolio
Current loans	224,937	275,039
Loans and Leases Receivable, Net of Deferred Income, Total	224,937	275,039
Residential real estate
Aging analysis of loan portfolio
Past due loans	728	921
Current loans	329,682	234,838
Loans and Leases Receivable, Net of Deferred Income, Total	330,410	235,759
Residential real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans		40
Residential real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	194
Residential real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	534	881
Multi-family and healthcare financing
Aging analysis of loan portfolio
Current loans	529,259	261,031
Loans and Leases Receivable, Net of Deferred Income, Total	529,259	261,031
Commercial and commercial real estate
Aging analysis of loan portfolio
Past due loans	2,921	2,960
Current loans	225,747	110,852
Loans and Leases Receivable, Net of Deferred Income, Total	228,668	113,812
Commercial and commercial real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans		43
Commercial and commercial real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	860	2,018
Commercial and commercial real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	2,061	899
Agricultural production and real estate
Aging analysis of loan portfolio
Past due loans	458	294
Current loans	51,508	46,469
Loans and Leases Receivable, Net of Deferred Income, Total	51,966	46,763
Agricultural production and real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	59	101
Agricultural production and real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans		86
Agricultural production and real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	399	107
Consumer and margin loans
Aging analysis of loan portfolio
Past due loans	146
Current loans	9,274	9,392
Loans and Leases Receivable, Net of Deferred Income, Total	9,420	$ 9,392
Consumer and margin loans | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	$ 146