Loans Held for Investment - Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Loans Held for Investment
Unpaid Principal Balance	$ 10,082	$ 6,896
Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	1,523	1,585
Business loans | Commercial owner occupied
Loans Held for Investment
Unpaid Principal Balance		98
Business loans | SBA
Loans Held for Investment
Unpaid Principal Balance	4,926	4,329
Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Unpaid Principal Balance	1,287
Real estate loans | One-to-four family
Loans Held for Investment
Unpaid Principal Balance	1,502	849
Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	16
Acquired Banks
Loans Held for Investment
Unpaid Principal Balance	5,140	8,889
Acquired Banks | Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	3,026	3,310
Acquired Banks | Business loans | Commercial owner occupied
Loans Held for Investment
Unpaid Principal Balance	769	1,262
Acquired Banks | Business loans | SBA
Loans Held for Investment
Unpaid Principal Balance	11	1,802
Acquired Banks | Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Unpaid Principal Balance	1,247	1,650
Acquired Banks | Real estate loans | One-to-four family
Loans Held for Investment
Unpaid Principal Balance	0	255
Acquired Banks | Real estate loans | Construction
Loans Held for Investment
Unpaid Principal Balance	0	517
Acquired Banks | Real estate loans | Land
Loans Held for Investment
Unpaid Principal Balance	79	83
Acquired Banks | Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	$ 8	$ 10