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Loans and Allowance for Loan Losses - Summary of Loans By Classification (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Loans and Allowance for Loan Losses
Loans	$ 2,755,793		$ 2,058,127
Allowance for loan losses	13,705	$ 12,604	12,704	$ 11,243	$ 10,588	$ 8,311
Loans and Leases Receivable, Net Amount, Total	2,742,088		2,045,423
Mortgage warehouse lines of credit
Loans and Allowance for Loan Losses
Loans	796,344		337,332
Allowance for loan losses	1,991	1,565	1,068	719	646	283
Residential real estate
Loans and Allowance for Loan Losses
Loans	410,550		410,871
Allowance for loan losses	1,992	1,929	1,986	1,892	1,812	1,587
Multi-family and healthcare financing
Loans and Allowance for Loan Losses
Loans	1,145,646		914,393
Allowance for loan losses	5,897	5,144	6,030	4,902	4,662	3,502
Commercial and commercial real estate
Loans and Allowance for Loan Losses
Loans	297,788		299,194
Allowance for loan losses	3,112	3,271	3,051	3,032	2,803	2,362
Agricultural production and real estate
Loans and Allowance for Loan Losses
Loans	85,737		79,255
Allowance for loan losses	529	515	429	427	392	320
Consumer and margin loans
Loans and Allowance for Loan Losses
Loans	19,728		17,082
Allowance for loan losses	$ 184	$ 180	$ 140	$ 271	$ 273	$ 257