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Loans and Allowance for Loan Losses - Summary of Loans By Classification (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Loans and Allowance for Loan Losses
Loans	$ 1,834,279		$ 1,374,660
Allowance for loan losses	10,588	$ 9,705	8,311	$ 6,865	$ 6,550	$ 6,250
Loans and Leases Receivable, Net Amount, Total	1,823,691		1,366,349
Mortgage warehouse lines of credit
Loans and Allowance for Loan Losses
Loans	397,852		224,937
Allowance for loan losses	646	506	283	281	181	373
Residential real estate
Loans and Allowance for Loan Losses
Loans	380,228		330,410
Allowance for loan losses	1,812	1,664	1,587	1,938	1,928	2,170
Multi-family and healthcare financing
Loans and Allowance for Loan Losses
Loans	703,305		529,259
Allowance for loan losses	4,662	4,250	3,502	2,426	2,097	1,962
Commercial and commercial real estate
Loans and Allowance for Loan Losses
Loans	271,661		228,668
Allowance for loan losses	2,803	2,685	2,362	1,845	1,918	1,374
Agricultural production and real estate
Loans and Allowance for Loan Losses
Loans	69,204		51,966
Allowance for loan losses	392	333	320	271	306	269
Consumer and margin loans
Loans and Allowance for Loan Losses
Loans	12,029		9,420
Allowance for loan losses	$ 273	$ 267	$ 257	$ 104	$ 120	$ 102