Employee Benefit Plans (Present Value of Accrued Liability) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Executives Directors And Officer Of Acquired Entities [Member]
Present Value Of Accrued Liability [Roll Forward]
Present value of accrued liability as of January 1	$ 38,597	$ 39,878
Benefit expense and interest cost	3,262	3,232
Benefits paid	4,560	4,194
Benefits forfeited	0	(319)
Present value of accrued liability as of December 31	37,299	38,597	$ 39,878
BancShares Plan
Present Value Of Accrued Liability [Roll Forward]
Benefit expense and interest cost	8,569	11,936	19,446
Interest cost	$ 28,940	$ 28,892	$ 26,975
Discount rate	3.76%	4.30%