Employee Benefit Plans Employee Benefit Plans 11 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Healthcare Cost Trend Rate
Initial health care cost for employees under age of 65 (as a percent)	6.20%
Ultimate health care cost for employees under age of 65 (as a percent)	4.50%
Initial Health care cost for employees of age 65 and over (as a percent)	6.20%
Ultimate health care cost for employees of age 65 and over (as a percent)	4.40%
Effects of one-percentage-point change in assumed health care cost trend rates
Effect on total of service and interest cost components -1 Percentage Point Increase	$ 45
Effect on total of service and interest cost components -1 Percentage Point Decrease	(39)
Effect on post-retirement benefit obligation -1 Percentage Point Increase	894
Effect on post-retirement benefit obligation -1 Percentage Point Decrease	$ (769)
Union plan
Employee benefit plans
Expected long-term return on plan assets	6.00%	[1]	7.00%	7.00%
Non-union plan
Employee benefit plans
Expected long-term return on plan assets	4.20%	[1]	4.20%	4.20%

[1] *6.0% for union plan and 4.2% for non-union (net of income taxes) in 2017, and 7.00% for union plan and 4.20% for non-union (net of income taxes) for 2016 and 2015.