Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax provision on comprehensive income	$ (31)	$ 8,080
Reclassifications out of other comprehensive income (loss) | Retirement plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of gain/loss and settlement loss	(120)	2,042
Income tax provision on comprehensive income	(31)	776
Total	$ (89)	$ 1,266