Retirement Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,265	$ 3,363
Interest cost	4,988	4,619
Expected return on plan assets	(8,891)	(8,213)
Amortization of net loss	1,468	644
Net periodic benefit cost	830	413
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	29	50
Interest cost	206	369
Amortization of net loss	(31)	125
Net periodic benefit cost	$ 204	$ 544