Covered Assets and Indemnification Asset - Internal Risk Grades (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Internal risk grades of covered loans in the portfolio
Total loans	$ 6,384,660	$ 6,273,669
Covered
Internal risk grades of covered loans in the portfolio
Total loans	160,970	182,129
Covered | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	75,473	87,113
Covered | Pass
Internal risk grades of covered loans in the portfolio
Total loans	67,990	81,583
Covered | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	343	356
Covered | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	17,164	13,077
Covered | Secured
Internal risk grades of covered loans in the portfolio
Total loans	938	1,055
Covered | Secured | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	147	194
Covered | Secured | Pass
Internal risk grades of covered loans in the portfolio
Total loans	392	429
Covered | Secured | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	399	432
Covered | Secured by Commercial Properties
Internal risk grades of covered loans in the portfolio
Total loans	27,351	35,353
Covered | Secured by Commercial Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	17,383	23,559
Covered | Secured by Commercial Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	9,208	10,961
Covered | Secured by Commercial Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	760	833
Covered | Secured by Residential Properties
Internal risk grades of covered loans in the portfolio
Total loans	131,321	144,006
Covered | Secured by Residential Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	57,943	63,356
Covered | Secured by Residential Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	57,048	68,544
Covered | Secured by Residential Properties | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	343	356
Covered | Secured by Residential Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	15,987	11,750
Covered | Commercial construction loans and land development
Internal risk grades of covered loans in the portfolio
Total loans	1,360	1,715
Covered | Commercial construction loans and land development | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans		4
Covered | Commercial construction loans and land development | Pass
Internal risk grades of covered loans in the portfolio
Total loans	1,342	1,649
Covered | Commercial construction loans and land development | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	$ 18	$ 62