Pensions and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated actuarial items that will be amortized from AOCI loss	$ 600
Ultimate health care cost trend rate	4.00%
Defined benefit plan, employer contribution in 2016	$ 1,300
Defined contribution plan matching expense	700	$ 600	$ 600
Accrued pension and other postretirement costs	14,713	11,597
Non Qualified Deferred Compensation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets held-in-trust	3,200	3,100
Accrued pension and other postretirement costs	4,100	3,800
Other Retirement Obligations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other retirement obligations	800	700
Non Qualified Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets held-in-trust	1,600	1,600
Non qualified pension plan liabilities	$ 2,000	$ 2,000