Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	$ 2,939	$ 3,091	$ 8,819	$ 9,272
Interest cost	6,553	6,544	19,658	19,631
Expected return on plan assets	(7,062)	(7,890)	(21,186)	(23,671)
Amortization of prior service cost	62	62	185	185
Recognized actuarial loss	2,472	2,659	7,416	7,976
Net Periodic Benefit Cost (Income)	4,964	4,466	14,892	13,393
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	123	132	369	395
Interest cost	198	197	596	590
Expected return on plan assets	(261)	(242)	(782)	(727)
Amortization of prior service cost	(471)	(471)	(1,412)	(1,412)
Recognized actuarial loss	78	96	236	289
Net Periodic Benefit Cost (Income)	$ (333)	$ (288)	$ (993)	$ (865)