Acquisitions and Divestiture (Narrative) (Details) $ in Thousands				9 Months Ended
	Mar. 09, 2018 USD ($)	Apr. 28, 2017 USD ($)	Mar. 10, 2017 USD ($) entity	Sep. 30, 2018 USD ($)	Jul. 13, 2018 USD ($)
Business Acquisition [Line Items]
Acquisition related costs				$ 5,700
Useful life				17 years
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
FNBC I [Member] | Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity			9
Net of cash acquired			$ 323,000
Cash paid			326,000
Cash acquired			3,000
Acquisition, Premium amount to pay			$ 41,600
FNBC II [Member] | 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
Capital One [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				$ 27,377
Assets under management					$ 4,000,000
Assets under management and administration					10,400,000
Cash for customer deposit liabilities assumed					$ 217,000