Commitments and Contingencies - Outstanding Commitments to Extend Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Total outstanding commitments	$ 990,030	$ 713,202
Commercial business
Other Commitments [Line Items]
Total outstanding commitments	594,901	383,630
Commercial business | Commercial and industrial
Other Commitments [Line Items]
Total outstanding commitments	568,215	363,272
Commercial business | Owner-occupied commercial real estate
Other Commitments [Line Items]
Total outstanding commitments	13,065	6,815
Commercial business | Non-owner occupied commercial real estate
Other Commitments [Line Items]
Total outstanding commitments	13,621	13,543
One-to-four family residential
Other Commitments [Line Items]
Total outstanding commitments	0	0
Real estate construction and land development
Other Commitments [Line Items]
Total outstanding commitments	155,307	124,947
Real estate construction and land development | One-to-four family residential
Other Commitments [Line Items]
Total outstanding commitments	59,772	38,160
Real estate construction and land development | Five or more family residential and commercial properties
Other Commitments [Line Items]
Total outstanding commitments	95,535	86,787
Consumer
Other Commitments [Line Items]
Total outstanding commitments	$ 239,822	$ 204,625