Pension Benefit and Retirement Health and Life Insurance Benefits (Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent assets	$ 2,583	$ 1,273
Current liabilities	0	(1)
Noncurrent liabilities	(8,501)	(12,624)
Net amount recognized at end of year	(5,918)	(11,352)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net actuarial (loss) gain	(59,377)	(62,972)
Prior service benefit	0	0
Net amount recognized at end of year	(59,377)	(62,972)
Retirement Health and Life Insurance Benefits
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent assets	0	0
Current liabilities	(150)	(537)
Noncurrent liabilities	(1,992)	(2,185)
Net amount recognized at end of year	(2,142)	(2,722)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Net actuarial (loss) gain	523	643
Prior service benefit	3,878	5,368
Net amount recognized at end of year	$ 4,401	$ 6,011