Retirement Plans (Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net actuarial loss (gain)	$ 12,079	$ (2,438)	$ 54,136
Reversal of amortization of net actuarial loss	(6,462)	(7,077)	(1,902)
Retirement Income Plan [Member]
Service cost	1,647	7,215	5,763
Interest cost	12,336	13,668	12,776
Expected return on plan assets	(17,309)	(15,969)	(15,671)
Amortization of unrecognized actuarial loss	6,299	6,831	1,776
Total net periodic cost	2,973	11,745	4,644
Net actuarial loss (gain)	11,316	(1,425)	52,556
Reversal of amortization of net actuarial loss	(6,299)	(6,831)	(1,776)
Total recognized in other comprehensive income	5,017	(8,256)	50,780
Total recognized in net periodic benefit cost and OCI	7,990	3,489	55,424
Estimated net actuarial loss that will be amortized from AOCI into net periodic benefit cost	1,900
Retirement Life Plan [Member]
Total net periodic cost	300		400
Supplemental Employee Retirement Plan [Member]
Total net periodic cost	$ 500	$ 800	$ 600