Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 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	$ 1,725	$ 3,063
Interest cost	1,780	1,642
Expected return on plan assets	(5,065)	(5,350)
Prior service cost	13	13
Actuarial (gain) loss	482	532
Total net pension cost	(1,065)	(100)
Other Postretirement Benefit Plan [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	36	35
Total net pension cost	$ 36	$ 35