Covered Assets and Indemnification Asset - Internal Risk Grades (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Internal risk grades of covered loans in the portfolio
Total loans	$ 6,216,809	$ 6,273,669
Covered
Internal risk grades of covered loans in the portfolio
Total loans	170,604	182,129
Covered | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	79,785	87,113
Covered | Pass
Internal risk grades of covered loans in the portfolio
Total loans	72,502	81,583
Covered | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	350	356
Covered | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	17,967	13,077
Covered | Secured
Internal risk grades of covered loans in the portfolio
Total loans	960	1,055
Covered | Secured | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	140	194
Covered | Secured | Pass
Internal risk grades of covered loans in the portfolio
Total loans	405	429
Covered | Secured | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	415	432
Covered | Secured by Commercial Properties
Internal risk grades of covered loans in the portfolio
Total loans	28,640	35,353
Covered | Secured by Commercial Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	17,711	23,559
Covered | Secured by Commercial Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	10,124	10,961
Covered | Secured by Commercial Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	805	833
Covered | Secured by Residential Properties
Internal risk grades of covered loans in the portfolio
Total loans	139,437	144,006
Covered | Secured by Residential Properties | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	61,930	63,356
Covered | Secured by Residential Properties | Pass
Internal risk grades of covered loans in the portfolio
Total loans	60,430	68,544
Covered | Secured by Residential Properties | Special Mention
Internal risk grades of covered loans in the portfolio
Total loans	350	356
Covered | Secured by Residential Properties | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	16,727	11,750
Covered | Commercial construction loans and land development
Internal risk grades of covered loans in the portfolio
Total loans	1,567	1,715
Covered | Commercial construction loans and land development | PCI loans
Internal risk grades of covered loans in the portfolio
Total loans	4	4
Covered | Commercial construction loans and land development | Pass
Internal risk grades of covered loans in the portfolio
Total loans	1,543	1,649
Covered | Commercial construction loans and land development | Substandard
Internal risk grades of covered loans in the portfolio
Total loans	$ 20	$ 62