Stockholders' Equity Reclassifications Out of Accumulated Other Comprehensive Income (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Amortization of Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss, before tax	$ (9,700)
Amortization of Actuarial Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss, before tax	36,990
Accumulated Postretirement Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss, before tax	(32,737)
Pension Settlement Charge [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss, before tax	102,109
Total Reclassifications [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss, before tax	96,662
Income tax expense	38,592
Total reclassification, net of tax	$ 58,070