Loans and Allowance for Loan Losses - Credit Risk Profile of Loan Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Credit risk profile of portfolio
Loans	$ 3,028,310	$ 2,058,127
Special Mention (Watch)
Credit risk profile of portfolio
Loans	60,305	90,604
Substandard
Credit risk profile of portfolio
Loans	12,517	11,185
Acceptable and Above
Credit risk profile of portfolio
Loans	2,955,488	1,956,338
Mortgage warehouse lines of credit
Credit risk profile of portfolio
Loans	765,151	337,332
Mortgage warehouse lines of credit | Substandard
Credit risk profile of portfolio
Loans	233	575
Mortgage warehouse lines of credit | Acceptable and Above
Credit risk profile of portfolio
Loans	764,918	336,757
Residential real estate
Credit risk profile of portfolio
Loans	413,835	410,871
Residential real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	2,472	443
Residential real estate | Substandard
Credit risk profile of portfolio
Loans	3,109	1,606
Residential real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	408,254	408,822
Multi-family and healthcare financing
Credit risk profile of portfolio
Loans	1,347,125	914,393
Multi-family and healthcare financing | Special Mention (Watch)
Credit risk profile of portfolio
Loans	41,882	71,734
Multi-family and healthcare financing | Acceptable and Above
Credit risk profile of portfolio
Loans	1,305,243	842,659
Commercial and commercial real estate
Credit risk profile of portfolio
Loans	398,601	299,194
Commercial and commercial real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	13,806	14,650
Commercial and commercial real estate | Substandard
Credit risk profile of portfolio
Loans	9,152	8,576
Commercial and commercial real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	375,643	275,968
Agricultural production and real estate
Credit risk profile of portfolio
Loans	85,210	79,255
Agricultural production and real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	2,114	3,096
Agricultural production and real estate | Substandard
Credit risk profile of portfolio
Loans		370
Agricultural production and real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	83,096	75,789
Consumer and margin loans
Credit risk profile of portfolio
Loans	18,388	17,082
Consumer and margin loans | Special Mention (Watch)
Credit risk profile of portfolio
Loans	31	681
Consumer and margin loans | Substandard
Credit risk profile of portfolio
Loans	23	58
Consumer and margin loans | Acceptable and Above
Credit risk profile of portfolio
Loans	$ 18,334	$ 16,343