Allowance for Loan Losses Activity in the allowance for loan losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan and Lease Losses, Reserve Estimate Methodology, Historical Loss Period Factor	120 months	120 months	108 months
Allowance for loan losses		$ 56,679	$ 51,512	$ 49,988	$ 50,624
Financing Receivable, Allowance for Credit Losses, Write-downs		11,177	13,552	19,403
Financing Receivable, Allowance for Credit Losses, Recovery		10,173	7,131	10,210
Financing Receivables Allowance For Credit Losses Net Charge Offs		1,004	6,421	9,193
Provision for Loan, Lease, and Other Losses		6,171	7,945	8,557
Commercial Financial And Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		20,203	16,777	15,022	13,434
Financing Receivable, Allowance for Credit Losses, Write-downs		2,231	2,796	6,017
Financing Receivable, Allowance for Credit Losses, Recovery		1,241	1,221	809
Financing Receivables Allowance For Credit Losses Net Charge Offs		990	1,575	5,208
Provision for Loan, Lease, and Other Losses		4,416	3,330	6,796
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		10,229	9,768	9,601	10,432
Financing Receivable, Allowance for Credit Losses, Write-downs		400	281	1,798
Financing Receivable, Allowance for Credit Losses, Recovery		720	272	810
Financing Receivables Allowance For Credit Losses Net Charge Offs		(320)	9	988
Provision for Loan, Lease, and Other Losses		141	176	157
Construction Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		5,311	4,463	4,430	5,247
Financing Receivable, Allowance for Credit Losses, Write-downs		0	72	105
Financing Receivable, Allowance for Credit Losses, Recovery		2,682	712	2,124
Financing Receivables Allowance For Credit Losses Net Charge Offs		(2,682)	(640)	(2,019)
Provision for Loan, Lease, and Other Losses		(1,834)	(607)	(2,836)
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		8,610	8,731	9,321	10,958
Financing Receivable, Allowance for Credit Losses, Write-downs		239	441	1,208
Financing Receivable, Allowance for Credit Losses, Recovery		787	844	1,863
Financing Receivables Allowance For Credit Losses Net Charge Offs		(548)	(403)	(655)
Provision for Loan, Lease, and Other Losses		(669)	(993)	(2,292)
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		12,211	11,773	11,614	10,553
Financing Receivable, Allowance for Credit Losses, Write-downs		8,307	9,962	10,275
Financing Receivable, Allowance for Credit Losses, Recovery		4,742	4,078	4,603
Financing Receivables Allowance For Credit Losses Net Charge Offs		3,565	5,884	5,672
Provision for Loan, Lease, and Other Losses		4,003	6,043	6,733
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses		115	0	0	$ 0
Financing Receivable, Allowance for Credit Losses, Write-downs		0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery		1	4	1
Financing Receivables Allowance For Credit Losses Net Charge Offs		(1)	(4)	(1)
Provision for Loan, Lease, and Other Losses		$ 114	$ (4)	$ (1)