Acquisitions and Divestitures - Purchase Price Allocation (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Jul. 17, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Consideration paid:
Goodwill	$ 1,510,431		$ 1,432,787	$ 1,432,787	$ 1,432,787
IBERIABANK (IBKC)
Assets:
Cash and due from banks	129,553
Interest-bearing deposits with banks	1,947,933
Securities available for sale at fair value	3,544,364
Loans held for sale	319,743
Loans and leases (a)	25,917,828
Allowance for loan and lease losses	(284,457)
Other intangible assets	237,763
Premises and equipment	310,617
Other real estate owned ("OREO")	8,593
Other assets	1,126,786
Total assets acquired	33,258,723
Liabilities:
Deposits	28,231,609
Short-term borrowings	208,733
Term borrowings	1,199,533
Other liabilities	585,143
Total liabilities assumed	30,225,018
Net assets acquired	3,033,705
Consideration paid:
Consideration for outstanding common stock	28,291
Cash in lieu of fractional shares	12
Total consideration paid	2,501,555
Goodwill	(532,150)
IBERIABANK (IBKC) | Commercial | Sales-Type And Direct Financing Leases
Assets:
Loans and leases (a)	1,300,000
IBERIABANK (IBKC) | Preferred Stock
Consideration paid:
Consideration for outstanding common stock	230,641
IBERIABANK (IBKC) | Common Stock
Consideration paid:
Consideration for outstanding common stock	2,242,611
SunTrust Banks, Inc. Branches
Assets:
Cash and due from banks	2,201,685
Loans and leases (a)	423,397
Allowance for loan and lease losses	2,355
Other intangible assets	7,000
Premises and equipment	10,965
Other assets	27,700
Total assets acquired	2,668,392
Liabilities:
Deposits	2,194,870	$ 2,200,000
Other liabilities	29,733
Total liabilities assumed	2,224,603
Net assets acquired	443,789
Consideration paid:
Cash in lieu of fractional shares	521,433
Total consideration paid	521,433
Goodwill	$ 77,644