Covered Assets and Indemnification Asset - Covered Loans Summary (Details) $ in Thousands	Sep. 13, 2013 USD ($)	Sep. 30, 2018 USD ($) item	Dec. 31, 2017 USD ($)
Covered Loans
Allowance for covered loans		$ (1,291)	$ (2,729)
Total covered loans, net of allowance		142,737	179,400
Covered
Covered Loans
Total covered loans		144,028	182,129
Allowance for covered loans		(1,291)	(2,729)
Total covered loans, net of allowance		142,737	179,400
Covered | Commercial and industrial
Covered Loans
Total covered loans		890	1,055
Covered | Real estate
Covered Loans
Total covered loans		141,858	179,359
Covered | Construction and land development
Covered Loans
Total covered loans		$ 1,280	$ 1,715
Covered | Acquired loans
Loans
Fair value of loans acquired	$ 1,100,000
Carryover of the allowance for loan losses recorded	$ 0
Minimum number of layers of common risk | item		2