Loans - Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Loans | Commercial and industrial
Loans Held for Investment
Total purchase credit impaired	$ 1,585	$ 1,990	$ 578
Business Loans | Commercial owner occupied
Loans Held for Investment
Total purchase credit impaired	98	847	883
Business Loans | SBA
Loans Held for Investment
Total purchase credit impaired	4,329	3,865
Real Estate Loans
Loans Held for Investment
Total purchase credit impaired	6,896	7,029	4,319
Real Estate Loans | Commercial non-owner occupied
Loans Held for Investment
Total purchase credit impaired	0	0	329
Real Estate Loans | One-to-four family
Loans Held for Investment
Total purchase credit impaired	849	291	98
Real Estate Loans | Construction
Loans Held for Investment
Total purchase credit impaired	0
Real Estate Loans | Land
Loans Held for Investment
Total purchase credit impaired	35	36	$ 37
Acquired Banks
Loans Held for Investment
Total purchase credit impaired	8,889	4,559
Acquired Banks | Business Loans
Loans Held for Investment
Total purchase credit impaired	6,374	3,077
Acquired Banks | Business Loans | Commercial and industrial
Loans Held for Investment
Total purchase credit impaired	3,310	2,586
Acquired Banks | Business Loans | Commercial owner occupied
Loans Held for Investment
Total purchase credit impaired	1,262	491
Acquired Banks | Business Loans | SBA
Loans Held for Investment
Total purchase credit impaired	1,802	0
Acquired Banks | Real Estate Loans
Loans Held for Investment
Total purchase credit impaired	2,505	1,089
Acquired Banks | Real Estate Loans | Commercial non-owner occupied
Loans Held for Investment
Total purchase credit impaired	1,650	1,088
Acquired Banks | Real Estate Loans | One-to-four family
Loans Held for Investment
Total purchase credit impaired	255	1
Acquired Banks | Real Estate Loans | Construction
Loans Held for Investment
Total purchase credit impaired	517	0
Acquired Banks | Real Estate Loans | Land
Loans Held for Investment
Total purchase credit impaired	83	0
Acquired Banks | Consumer Loans | Consumer loans
Loans Held for Investment
Total purchase credit impaired	$ 10	$ 393