Acquisitions and Divestiture (Schedule of Fair Value of Net Assets Acquired Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 855,453	$ 790,972	$ 745,523
MidSouth [Member]
Business Acquisition [Line Items]
Cash and due from banks	28,059
Interest bearing bank deposits	276,911
Federal funds sold	3,475
Securities available for sale	272,240
Loans	787,628
Property and equipment	34,288
Other real estate	343
Identifiable intangible assets	31,500
Other assets	79,888
Total identifiable assets	1,514,332
Deposit liabilities	1,280,947
Short term borrowings	66,996
Long term debt	13,919
Other liabilities	21,990
Total liabilities	1,383,852
Net identifiable assets acquired (liabilities assumed)	130,480
Value of stock-based consideration	193,849
Goodwill	$ 63,369