Employee Benefit Plans (Summary of the Activity in the SERP's Projected Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Benefit obligation:
Balance, January 1	$ 78,369	$ 81,342
Service cost	3,559	3,795
Interest cost	3,505	3,178
Benefits paid	(1,885)	(1,588)
Actuarial (gain) loss	2,003	(8,358)
Balance, December 31	85,551	78,369	$ 81,342
Supplemental Executive Retirement Plan [Member]
Benefit obligation:
Balance, January 1	8,748	9,403
Service cost	133	140	136
Interest cost	367	348	377
Benefits paid	(247)	(243)	(236)
Actuarial (gain) loss	131	(900)
Balance, December 31	$ 9,132	$ 8,748	$ 9,403