Acquisitions and Divestiture (Schedule of Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill, Beginning Balance	$ 790,972	$ 745,523
Goodwill, Ending Balance	855,453	790,972
Trust And Asset Management Acquisition [Member]
Business Acquisition [Line Items]
Goodwill, Beginning Balance	46,600
Final settlement of cash consideration - acquisition of trust and asset management business	1,112
Goodwill, Initial goodwill recorded		45,634
Goodwill, Measurement period adjustments		(185)
Goodwill, Ending Balance		$ 46,600
MidSouth [Member]
Business Acquisition [Line Items]
Goodwill, Initial goodwill recorded	69,207
Goodwill, Measurement period adjustments	(5,838)
Goodwill, Ending Balance	$ 63,369