Loans Held for Investment - Purchased Credit Impaired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Loans Held for Investment
Total purchased credit impaired	$ 17,210	$ 17,440
Business loans | Commercial and industrial
Loans Held for Investment
Total purchased credit impaired	3,099	1,071
Business loans | Commercial owner occupied
Loans Held for Investment
Total purchased credit impaired	1,427	628
Business loans | SBA
Loans Held for Investment
Total purchased credit impaired	3,320	7,598
Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Total purchased credit impaired	1,351
Acquired Banks
Loans Held for Investment
Total purchased credit impaired	1,731	2,182
Acquired Banks | Business loans | Commercial and industrial
Loans Held for Investment
Total purchased credit impaired	0	10
Acquired Banks | Business loans | Commercial owner occupied
Loans Held for Investment
Total purchased credit impaired	577	632
Acquired Banks | Business loans | SBA
Loans Held for Investment
Total purchased credit impaired	1,154	1,265
Acquired Banks | Real estate loans | Commercial non-owner occupied
Loans Held for Investment
Total purchased credit impaired	$ 0	$ 275