Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Net period benefit cost for the pension and postretirement plans
Service cost	$ 11,257	$ 11,058	$ 12,078
Interest cost	6,617	7,132	6,237
Expected return on plan assets	(21,438)	(19,922)	(17,647)
Prior service cost	50	58	72
Actuarial (gain) loss	2,256	1,384	4,344
Total net pension cost	(1,258)	(290)	5,084
Other Postretirement Benefit Plan [Member]
Net period benefit cost for the pension and postretirement plans
Service cost	0	0	0
Interest cost	141	150	142
Prior service cost	0	0	0
Actuarial (gain) loss	0	(35)	0
Total net pension cost	$ 141	$ 115	$ 142