Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	$ 3,130	$ 2,939
Interest cost	6,429	6,566
Expected return on plan assets	(6,008)	(7,081)
Amortization of prior service cost	2	62
Recognized actuarial loss	1,975	2,466
Net Periodic Benefit Cost (Income)	5,528	4,952
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	128	130
Interest cost	180	202
Expected return on plan assets	(213)	(261)
Amortization of prior service cost	(471)	(471)
Recognized actuarial loss	78	87
Net Periodic Benefit Cost (Income)	$ (298)	$ (313)