Acquisitions and Divestiture (Narrative) (Details) shares in Millions			12 Months Ended
	Sep. 21, 2019 USD ($) shares	Mar. 09, 2018 USD ($)	Dec. 31, 2019 USD ($) loan shares	Dec. 31, 2018 USD ($)	Jul. 13, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 855,453,000	$ 790,972,000		$ 745,523,000
Purchased credit impaired loans book balance			287,767,000	308,401,000
Recorded investment without an allowance			$ 104,560,000	107,528,000
Estimated useful life			17 years
Harrison Finance Company [Member]
Business Acquisition [Line Items]
Proceeds from sale of finance subsidiary		$ 78,900,000
Loss from sale of consumer finance subsidiary		$ 1,100,000
MidSouth [Member]
Business Acquisition [Line Items]
Net assets acquired			$ 130,480,000
Goodwill			$ 63,369,000
Common stock issued | shares	5,044,332.0		5.0
Business combination transaction value on an average of share price	$ 193,800,000		$ 193,800,000
Maximum period for adjustments to provisional fair value measurements			1 year
Book balance of the loans acquired			$ 686,000,000.0
Estimated uncollectible amount			18,800,000
Estimated fair value of uncollectible amount			667,100,000
Purchased credit impaired loans book balance			143,900,000
Recorded investment without an allowance			120,500,000
Identifiable intangible assets			$ 31,500,000
Estimated useful life			15 years
Customer repurchase agreements			$ 39,500,000
Number of preferred debentures			3
Debt instrument maturity year			2037
Acquisition related costs			$ 32,666,000
Assets under management			$ 787,628,000
MidSouth [Member] | FHLB
Business Acquisition [Line Items]
Number of FHLB advances | loan			2
FHLB advances amount			$ 27,500
FHLB advances maturity period			30 days
FHLB advances fixed interest rate			2.16%
Capital One [Member]
Business Acquisition [Line Items]
Net assets acquired			$ (187,218,000)
Goodwill			46,561,000
Identifiable intangible assets			$ 27,562,000
Assets under management					$ 4,000,000,000
Assets under management and administration					10,400,000,000
Cash for customer deposit liabilities assumed					$ 217,000,000
Trust And Asset Management Acquisition [Member]
Business Acquisition [Line Items]
Goodwill				46,600,000
Estimated useful life			17 years
Acquisition related costs				$ 6,200,000