Loans and Allowance for Loan Losses - Geographic and Collateral Concentration (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Concentration risk
Percentage of loan	100.00%	100.00%
Percentage of SBA loan	100.00%	100.00%
Offices of Physicians
Concentration risk
Percentage of SBA loan	13.40%	17.70%
Child Day Care Services
Concentration risk
Percentage of SBA loan	9.60%	9.90%
Hotels, Motels and Tourist Courts
Concentration risk
Percentage of SBA loan	9.00%	3.80%
Eating Places
Concentration risk
Percentage of SBA loan	7.10%	5.40%
Lodging
Concentration risk
Percentage of SBA loan	5.30%	10.10%
Veterinarians
Concentration risk
Percentage of SBA loan	4.80%	6.80%
Gasoline Service Stations
Concentration risk
Percentage of SBA loan	4.30%	2.30%
Funeral Service and Crematories
Concentration risk
Percentage of SBA loan	3.10%	2.30%
Grocery Stores
Concentration risk
Percentage of SBA loan	2.60%	3.80%
Auto
Concentration risk
Percentage of SBA loan	1.80%	2.70%
Other
Concentration risk
Percentage of SBA loan	39.00%	35.20%
Multi-family
Concentration risk
Percentage of loan	30.70%	23.30%
Retail
Concentration risk
Percentage of loan	19.40%	18.50%
Office
Concentration risk
Percentage of loan	14.30%	15.10%
Mixed Use
Concentration risk
Percentage of loan	12.30%	9.60%
SBA
Concentration risk
Percentage of loan	7.60%	18.10%
Industrial
Concentration risk
Percentage of loan	7.40%	8.20%
Lodging/Residential
Concentration risk
Percentage of loan	2.80%	2.40%
Other
Concentration risk
Percentage of loan	5.50%	4.80%
Geographical concentration
Concentration risk
Percentage of loan	100.00%	100.00%
Geographical concentration | California
Concentration risk
Percentage of loan	18.10%	14.10%
Geographical concentration | Texas
Concentration risk
Percentage of loan	15.30%	11.30%
Geographical concentration | New York
Concentration risk
Percentage of loan	7.90%	6.30%
Geographical concentration | Florida
Concentration risk
Percentage of loan	7.70%	10.80%
Geographical concentration | Illinois
Concentration risk
Percentage of loan	6.00%	3.80%
Geographical concentration | Arizona
Concentration risk
Percentage of loan	4.20%	5.00%
Geographical concentration | Georgia
Concentration risk
Percentage of loan	4.20%	5.30%
Geographical concentration | North Carolina
Concentration risk
Percentage of loan	3.10%	3.70%
Geographical concentration | Washington
Concentration risk
Percentage of loan	2.50%	2.80%
Geographical concentration | Ohio
Concentration risk
Percentage of loan	2.50%	2.80%
Geographical concentration | Other
Concentration risk
Percentage of loan	28.50%	34.10%