Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 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	$ 1,725	$ 3,062	$ 3,450	$ 6,125
Interest cost	1,780	1,643	3,560	3,285
Expected return on plan assets	(5,065)	(5,350)	(10,130)	(10,700)
Amortization of prior service cost	12	12	25	25
Amortization of actuarial loss	483	533	965	1,065
Total net pension cost	(1,065)	(100)	(2,130)	(200)
Other Postretirement Benefit Plan [Member]
Net period benefit cost for the pension and postretirement plans
Interest cost	36	35	72	70
Total net pension cost	$ 36	$ 35	$ 72	$ 70