Covered Assets and Indemnification Asset - Aging (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Covered Assets and Indemnification Asset
Total loans	$ 6,216,809	$ 6,273,669
Covered
Covered Assets and Indemnification Asset
Total Past Due Loans	8,811	10,421
Current Loans	82,008	84,595
Total loans	170,604	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	5,265	5,871
Covered | Financing Receivables, 60 to 89 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	641	1,324
Covered | Financing Receivables, Equal to Greater than 90 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	2,905	3,226
Covered | PCI loans
Covered Assets and Indemnification Asset
Total loans	79,785	87,113
Covered | Secured
Covered Assets and Indemnification Asset
Current Loans	820	861
Total loans	960	1,055
Covered | Secured | PCI loans
Covered Assets and Indemnification Asset
Total loans	140	194
Covered | Secured by Commercial Properties
Covered Assets and Indemnification Asset
Total Past Due Loans	146	322
Current Loans	10,783	11,472
Total loans	28,640	35,353
Covered | Secured by Commercial Properties | Financing Receivables, 30 to 59 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	146	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	17,711	23,559
Covered | Secured by Residential Properties
Covered Assets and Indemnification Asset
Total Past Due Loans	8,627	10,061
Current Loans	68,880	70,589
Total loans	139,437	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	5,119	5,624
Covered | Secured by Residential Properties | Financing Receivables, 60 to 89 Days Past Due
Covered Assets and Indemnification Asset
Total Past Due Loans	603	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	2,905	3,226
Covered | Secured by Residential Properties | PCI loans
Covered Assets and Indemnification Asset
Total loans	61,930	63,356
Covered | Commercial construction loans and land development
Covered Assets and Indemnification Asset
Total Past Due Loans	38	38
Current Loans	1,525	1,673
Total loans	1,567	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 | Financing Receivables, 60 to 89 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	$ 4