Loans and Allowance for Loan Losses - Aging Analysis Of The Recorded Investment In Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Aging analysis of loan portfolio
Past due loans	$ 5,874	$ 4,253
Current loans	1,567,316	1,370,407
Loans and Leases Receivable, Net of Deferred Income, Total	1,573,190	1,374,660
30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	845	59
60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	1,077	1,054
Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	3,952	3,140
Mortgage warehouse lines of credit
Aging analysis of loan portfolio
Past due loans	933
Current loans	244,791	224,937
Loans and Leases Receivable, Net of Deferred Income, Total	245,724	224,937
Mortgage warehouse lines of credit | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	933
Residential real estate
Aging analysis of loan portfolio
Past due loans	1,658	728
Current loans	355,227	329,682
Loans and Leases Receivable, Net of Deferred Income, Total	356,885	330,410
Residential real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	575
Residential real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	123	194
Residential real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	960	534
Multi-family and healthcare financing
Aging analysis of loan portfolio
Past due loans	116
Current loans	645,316	529,259
Loans and Leases Receivable, Net of Deferred Income, Total	645,432	529,259
Multi-family and healthcare financing | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	116
Commercial and commercial real estate
Aging analysis of loan portfolio
Past due loans	2,440	2,921
Current loans	246,932	225,747
Loans and Leases Receivable, Net of Deferred Income, Total	249,372	228,668
Commercial and commercial real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	120
Commercial and commercial real estate | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	15	860
Commercial and commercial real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	2,305	2,061
Agricultural production and real estate
Aging analysis of loan portfolio
Past due loans	538	458
Current loans	64,010	51,508
Loans and Leases Receivable, Net of Deferred Income, Total	64,548	51,966
Agricultural production and real estate | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	139	59
Agricultural production and real estate | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	399	399
Consumer and margin loans
Aging analysis of loan portfolio
Past due loans	189	146
Current loans	11,040	9,274
Loans and Leases Receivable, Net of Deferred Income, Total	11,229	9,420
Consumer and margin loans | 30-59 Days Past Due
Aging analysis of loan portfolio
Past due loans	11
Consumer and margin loans | 60-89 Days Past Due
Aging analysis of loan portfolio
Past due loans	6
Consumer and margin loans | Greater Than 90 Days
Aging analysis of loan portfolio
Past due loans	$ 172	$ 146