Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,072	$ 3,938	$ 4,594
Interest cost	6,342	6,098	5,393
Expected return on assets	(6,984)	(6,414)	(5,289)
Amortization of prior service cost	376	376	394
Recognized actuarial loss	4,005	1,879	4,052
Net periodic pension cost	8,811	5,877	9,144
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	379	284	361
Interest cost	504	508	508
Expected return on assets	(283)	(268)	(230)
Amortization of prior service cost	197	197	197
Recognized actuarial loss	188	59	189
Net periodic pension cost	$ 985	$ 780	$ 1,025