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Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)	Sep. 01, 2018 USD ($)	Jul. 01, 2017 USD ($)	Jul. 01, 2015 agreement
Financing Receivable, Impaired [Line Items]
Date of discontinued recognition of interest on mortgage and commercial loans	90 days
Consumer and other retail loan due date	120 days
Minimum duration for past due residential loans to be considered as nonperforming	90 days
Payments made to FDIC to terminate loss share agreements	$ 0	$ 0	$ 4,849,000
Impairment of company's goodwill	$ 0	$ 0	$ 0
Lock in period for interest rates	45 days
Subsequent Event | Accounting Standards Update 2016-02
Financing Receivable, Impaired [Line Items]
Operating Lease, Right-of-Use Asset				$ 55,000,000
Operating Lease, Liability				$ 55,000,000
Premises
Financing Receivable, Impaired [Line Items]
Estimated life (in years)	40 years
Furniture and equipment
Financing Receivable, Impaired [Line Items]
Estimated life (in years)	7 years
Computer equipment | Minimum
Financing Receivable, Impaired [Line Items]
Estimated life (in years)	3 years
Computer equipment | Maximum
Financing Receivable, Impaired [Line Items]
Estimated life (in years)	5 years
Heritage Financial Group
Financing Receivable, Impaired [Line Items]
Number of loss sharing agreements acquired | agreement							2
Brand Group Holdings, Inc.
Financing Receivable, Impaired [Line Items]
Cash surrender value of life insurance					$ 40,081,000
Metropolitan Bancgroup, Inc.
Financing Receivable, Impaired [Line Items]
Cash surrender value of life insurance						$ 19,283,000

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