Covered Assets and Indemnification Asset - Aging (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Covered Assets and Indemnification Asset
Total loans	$ 6,796,278	$ 6,273,669
Covered
Covered Assets and Indemnification Asset
Total Past Due Loans	5,255	10,421
Current Loans	73,769	84,595
Total loans	144,028	182,129
Accruing Loans Past Due 90 Days or More		283
Covered | Financing Receivables, 30 to 59 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	2,407	5,871
Covered | Financing Receivables, 60 to 89 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	555	1,324
Covered | Financing Receivables, Equal to Greater than 90 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	2,293	3,226
Covered | PCI loans
Covered Assets and Indemnification Asset
Total loans	65,004	87,113
Covered | Secured
Covered Assets and Indemnification Asset
Current Loans	760	861
Total loans	890	1,055
Covered | Secured | PCI loans
Covered Assets and Indemnification Asset
Total loans	130	194
Covered | Secured by Commercial Properties
Covered Assets and Indemnification Asset
Total Past Due Loans	65	322
Current Loans	8,799	11,472
Total loans	17,115	35,353
Covered | Secured by Commercial Properties | Financing Receivables, 30 to 59 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	65	209
Covered | Secured by Commercial Properties | Financing Receivables, 60 to 89 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans		113
Covered | Secured by Commercial Properties | PCI loans
Covered Assets and Indemnification Asset
Total loans	8,251	23,559
Covered | Secured by Residential Properties
Covered Assets and Indemnification Asset
Total Past Due Loans	5,190	10,061
Current Loans	62,930	70,589
Total loans	124,743	144,006
Accruing Loans Past Due 90 Days or More		283
Covered | Secured by Residential Properties | Financing Receivables, 30 to 59 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	2,342	5,624
Covered | Secured by Residential Properties | Financing Receivables, 60 to 89 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	555	1,211
Covered | Secured by Residential Properties | Financing Receivables, Equal to Greater than 90 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	2,293	3,226
Covered | Secured by Residential Properties | PCI loans
Covered Assets and Indemnification Asset
Total loans	56,623	63,356
Covered | Commercial construction loans and land development
Covered Assets and Indemnification Asset
Total Past Due Loans		38
Current Loans	1,280	1,673
Total loans	$ 1,280	1,715
Covered | Commercial construction loans and land development | Financing Receivables, 30 to 59 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans		38
Covered | Commercial construction loans and land development | PCI loans
Covered Assets and Indemnification Asset
Total loans		$ 4