Loans Held for Investment - Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loans Held for Investment
Unpaid Principal Balance	$ 12,739	$ 6,896
Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	1,515	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	7,618	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	1,476	849
Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	15
Acquired Banks
Loans Held for Investment
Unpaid Principal Balance	7,882	8,889
Acquired Banks | Business loans | Commercial and industrial
Loans Held for Investment
Unpaid Principal Balance	1,700	3,310
Acquired Banks | Business loans | Commercial owner occupied
Loans Held for Investment
Unpaid Principal Balance	2,808	1,262
Acquired Banks | Business loans | SBA
Loans Held for Investment
Unpaid Principal Balance	1,304	1,802
Acquired Banks | Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Unpaid Principal Balance	1,077	1,650
Acquired Banks | Real estate loans | One-to-four family
Loans Held for Investment
Unpaid Principal Balance	909	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	76	83
Acquired Banks | Consumer Loans | Consumer loans
Loans Held for Investment
Unpaid Principal Balance	$ 8	$ 10