Acquisitions and Divestiture (Narrative) (Details) $ in Thousands				12 Months Ended
	Mar. 09, 2018 USD ($)	Apr. 28, 2017 USD ($)	Mar. 10, 2017 USD ($) entity	Dec. 31, 2018 USD ($)	Jul. 13, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Total Loans					$ 10,400,000
Useful life				17 years
Unpaid principal balance				$ 308,401		$ 341,713
Recorded investment without an allowance				161,227		147,055
Recorded investment with an allowance				107,528		170,142
Short-term borrowings				1,589,128		1,703,890
Long-term debt				224,993		305,513
Hancock Whitney Bank [Member]
Business Acquisition [Line Items]
Net of cash acquired			$ 323,000
Cash consideration			326,000
Cash acquired			3,000
Acquisition, Premium amount to pay			41,600
FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings				1,160,104		1,132,567
Harrison Finance Company [Member]
Business Acquisition [Line Items]
Loss from sale of consumer finance subsidiary	$ 1,100
Proceeds from sale of finance subsidiary	$ 78,900
Capital One [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				27,562
Acquisition, debt assumed				151
Total Loans				4,000,000
Liabilities assumed				217,583
Cash for customer deposit liabilities assumed					$ 217,000
FNBC Transactions [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				25,300		25,300
Fair value discount				41,000
Acquisition, debt assumed						4,686
Total Loans						1,368,669
Unpaid principal balance of the loans acquired				1,400,000
Liabilities assumed						$ 2,622,950
Estimated uncollectible amount				31,700
Unpaid principal balance				39,900
Recorded investment without an allowance				24,900
Recorded investment with an allowance				$ 15,000
FNBC I [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			3,900
Acquisition, debt assumed			1,607
Total Loans			1,203,092
Useful life				8 years
Liabilities assumed			$ 1,003,647
FNBC I [Member] | Hancock Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity			9
FNBC I [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Liabilities assumed				$ 690,000
FNBC I [Member] | Variable-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings				460,000
FNBC I [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Long-term debt				93,100
FNBC I [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings				$ 51,000
FNBC II [Member]
Business Acquisition [Line Items]
Identifiable intangible assets		$ 21,400
Acquisition, debt assumed		3,079
Total Loans		165,577
Useful life				11 years
Liabilities assumed		1,619,303
FNBC II [Member] | Hancock Whitney Bank [Member]
Business Acquisition [Line Items]
Cash received		800,000
Cash acquired		158,000
Premium payment		35,000
Unpaid principal balance of the loans acquired, Net liabilities assumed		$ 642,000
Trust And Asset Management Acquisition [Member]
Business Acquisition [Line Items]
Trust fee revenue				$ 10,500
Related expense				$ 7,300