Loans and Allowance for Loan Losses - Credit Risk Profile of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Credit risk profile of portfolio
Loans	$ 1,209,152	$ 941,796
Special Mention (Watch)
Credit risk profile of portfolio
Loans	14,851	9,522
Substandard
Credit risk profile of portfolio
Loans	4,969	5,532
Acceptable and Above
Credit risk profile of portfolio
Loans	1,189,332	926,742
Mortgage warehouse lines of credit
Credit risk profile of portfolio
Loans	233,466	275,039
Mortgage warehouse lines of credit | Acceptable and Above
Credit risk profile of portfolio
Loans	233,466	275,039
Residential real estate
Credit risk profile of portfolio
Loans	307,643	235,759
Residential real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	209	214
Residential real estate | Substandard
Credit risk profile of portfolio
Loans	246	343
Residential real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	307,188	235,202
Multi-family and healthcare financing
Credit risk profile of portfolio
Loans	393,581	261,031
Multi-family and healthcare financing | Special Mention (Watch)
Credit risk profile of portfolio
Loans	1,800
Multi-family and healthcare financing | Acceptable and Above
Credit risk profile of portfolio
Loans	391,781	261,031
Commercial and commercial real estate
Credit risk profile of portfolio
Loans	210,421	113,812
Commercial and commercial real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	10,609	7,150
Commercial and commercial real estate | Substandard
Credit risk profile of portfolio
Loans	4,441	4,986
Commercial and commercial real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	195,371	101,676
Agricultural production and real estate
Credit risk profile of portfolio
Loans	51,925	46,763
Agricultural production and real estate | Special Mention (Watch)
Credit risk profile of portfolio
Loans	351
Agricultural production and real estate | Substandard
Credit risk profile of portfolio
Loans	282	203
Agricultural production and real estate | Acceptable and Above
Credit risk profile of portfolio
Loans	51,292	46,560
Consumer and margin loans
Credit risk profile of portfolio
Loans	12,116	9,392
Consumer and margin loans | Special Mention (Watch)
Credit risk profile of portfolio
Loans	1,882	2,158
Consumer and margin loans | Acceptable and Above
Credit risk profile of portfolio
Loans	$ 10,234	$ 7,234