Retirement Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,611	$ 3,383	$ 10,487	$ 10,128
Interest cost	4,022	4,672	13,033	13,963
Expected return on plan assets	(8,554)	(8,207)	(25,999)	(24,626)
Amortization of net loss	1,426	842	4,320	2,328
Net periodic benefit cost	505	690	1,841	1,793
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	45	23	119	95
Interest cost	204	174	613	717
Amortization of net loss	53	(40)	75	45
Net periodic benefit cost	$ 302	$ 157	$ 807	$ 857