Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Retirement Plans Textuals [Abstract]
Defined Benefit Plan, Age of Eligibility of Plan			55 years
Defined Benefit Plan, Service Period for Eligibility in Plan			5 years
Pension Plan [Member]
Net period benefit cost for the pension and postretirement plans
Service cost	$ 1,636	$ 2,318	$ 5,086	$ 8,443
Interest cost	1,781	1,678	5,341	4,963
Expected return on plan assets	(5,085)	(5,379)	(15,215)	(16,079)
Amortization of prior service cost	(80)	12	(55)	37
Amortization of actuarial loss	621	627	1,586	1,692
Total net pension cost	(1,127)	(744)	(3,257)	(944)
Other Postretirement Benefit Plan [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	35	35	107	105
Total net pension cost	$ 35	$ 35	$ 107	$ 105