Covered Assets and Indemnification Asset - Internal Risk Grades (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Internal risk grades of covered loans in the portfolio
Total loans	$ 6,796,278	$ 6,273,669
Covered
Internal risk grades of covered loans in the portfolio
Total loans	144,028	182,129
Covered | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	65,004	87,113
Covered | Pass
Internal risk grades of covered loans in the portfolio
Total loans	73,911	81,583
Covered | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	395	356
Covered | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	4,718	13,077
Covered | Secured
Internal risk grades of covered loans in the portfolio
Total loans	890	1,055
Covered | Secured | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	130	194
Covered | Secured | Pass
Internal risk grades of covered loans in the portfolio
Total loans	379	429
Covered | Secured | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	381	432
Covered | Secured by Commercial Properties
Internal risk grades of covered loans in the portfolio
Total loans	17,115	35,353
Covered | Secured by Commercial Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	8,251	23,559
Covered | Secured by Commercial Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	8,168	10,961
Covered | Secured by Commercial Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	696	833
Covered | Secured by Residential Properties
Internal risk grades of covered loans in the portfolio
Total loans	124,743	144,006
Covered | Secured by Residential Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	56,623	63,356
Covered | Secured by Residential Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	64,100	68,544
Covered | Secured by Residential Properties | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	395	356
Covered | Secured by Residential Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	3,625	11,750
Covered | Commercial construction loans and land development
Internal risk grades of covered loans in the portfolio
Total loans	1,280	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	1,264	1,649
Covered | Commercial construction loans and land development | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	$ 16	$ 62