Retirement Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,611	$ 3,382	$ 6,876	$ 6,745
Interest cost	4,023	4,672	9,011	9,291
Expected return on plan assets	(8,554)	(8,206)	(17,445)	(16,419)
Amortization of net loss	1,426	842	2,894	1,486
Net periodic benefit cost	506	690	1,336	1,103
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	45	22	74	72
Interest cost	203	174	409	543
Amortization of net loss	53	(40)	22	85
Net periodic benefit cost	$ 301	$ 156	$ 505	$ 700