Loans and Allowance for Loan Losses - Aging Analysis Of The Recorded Investment In Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Aging analysis of loan portfolio
Past due loans	$ 3,035	$ 4,253
Current loans	1,914,067	1,370,407
Loans and Leases Receivable, Net of Deferred Income, Total	1,917,102	1,374,660
30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	1,348	59
60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	98	1,054
Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	1,589	3,140
Mortgage warehouse lines of credit
Aging analysis of loan portfolio
Past due loans	324
Current loans	405,963	224,937
Loans and Leases Receivable, Net of Deferred Income, Total	406,287	224,937
Mortgage warehouse lines of credit | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	324
Residential real estate
Aging analysis of loan portfolio
Past due loans	1,550	728
Current loans	398,420	329,682
Loans and Leases Receivable, Net of Deferred Income, Total	399,970	330,410
Residential real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	1,111
Residential real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	80	194
Residential real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	359	534
Multi-family and healthcare financing
Aging analysis of loan portfolio
Current loans	738,879	529,259
Loans and Leases Receivable, Net of Deferred Income, Total	738,879	529,259
Commercial and commercial real estate
Aging analysis of loan portfolio
Past due loans	274	2,921
Current loans	289,852	225,747
Loans and Leases Receivable, Net of Deferred Income, Total	290,126	228,668
Commercial and commercial real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	109
Commercial and commercial real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans		860
Commercial and commercial real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	165	2,061
Agricultural production and real estate
Aging analysis of loan portfolio
Past due loans	659	458
Current loans	69,621	51,508
Loans and Leases Receivable, Net of Deferred Income, Total	70,280	51,966
Agricultural production and real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	71	59
Agricultural production and real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	588	399
Consumer and margin loans
Aging analysis of loan portfolio
Past due loans	228	146
Current loans	11,332	9,274
Loans and Leases Receivable, Net of Deferred Income, Total	11,560	9,420
Consumer and margin loans | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	57
Consumer and margin loans | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	18
Consumer and margin loans | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	$ 153	$ 146