Loans and Allowance for Loan Losses - Credit Risk Profile of Loan Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Credit risk profile of portfolio
Loans	$ 1,834,279	$ 1,374,660
Special Mention (Watch)
Credit risk profile of portfolio
Loans	52,399	16,294
Substandard
Credit risk profile of portfolio
Loans	9,351	7,336
Acceptable and Above
Credit risk profile of portfolio
Loans	1,772,529	1,351,030
Mortgage warehouse lines of credit
Credit risk profile of portfolio
Loans	397,852	224,937
Mortgage warehouse lines of credit | Substandard
Credit risk profile of portfolio
Loans	804
Mortgage warehouse lines of credit | Acceptable and Above
Credit risk profile of portfolio
Loans	397,048	224,937
Residential real estate
Credit risk profile of portfolio
Loans	380,228	330,410
Residential real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	306
Residential real estate | Substandard
Credit risk profile of portfolio
Loans	1,066	729
Residential real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	378,856	329,681
Multi-family and healthcare financing
Credit risk profile of portfolio
Loans	703,305	529,259
Multi-family and healthcare financing | Special Mention (Watch)
Credit risk profile of portfolio
Loans	34,637	1,800
Multi-family and healthcare financing | Substandard
Credit risk profile of portfolio
Loans	110
Multi-family and healthcare financing | Acceptable and Above
Credit risk profile of portfolio
Loans	668,558	527,459
Commercial and commercial real estate
Credit risk profile of portfolio
Loans	271,661	228,668
Commercial and commercial real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	13,208	12,608
Commercial and commercial real estate | Substandard
Credit risk profile of portfolio
Loans	6,539	6,179
Commercial and commercial real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	251,914	209,881
Agricultural production and real estate
Credit risk profile of portfolio
Loans	69,204	51,966
Agricultural production and real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	2,659	323
Agricultural production and real estate | Substandard
Credit risk profile of portfolio
Loans	636	282
Agricultural production and real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	65,909	51,361
Consumer and margin loans
Credit risk profile of portfolio
Loans	12,029	9,420
Consumer and margin loans | Special Mention (Watch)
Credit risk profile of portfolio
Loans	1,589	1,563
Consumer and margin loans | Substandard
Credit risk profile of portfolio
Loans	196	146
Consumer and margin loans | Acceptable and Above
Credit risk profile of portfolio
Loans	$ 10,244	$ 7,711