Accumulated Other Comprehensive Loss Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes		$ (20,525)	$ 21,381	$ (11,564)
Income tax benefit		63,134	(6,911)	242
Net income (loss)		42,609	14,470	(11,322)
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	[1]	(347)	(347)	(40,532)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior-service cost
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior-service cost	[1],[2]	(455)	(354)	(543)
Income (loss) before income taxes	[1]	(455)	(354)	(543)
Income tax benefit		108	133	204
Net income (loss)	[1]	$ (347)	(221)	(339)
Reclassification out of Accumulated Other Comprehensive Income | Recognition of gain on sale of investment
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior-service cost	[3]		200	64,939
Income (loss) before income taxes	[3]		(200)	(64,939)
Income tax benefit			74	24,746
Net income (loss)	[3]		$ (126)	$ (40,193)

[1] Amounts in parentheses indicate debits to profit/loss

[2] This accumulated other comprehensive income component is included in the computation of net periodic benefit cost (see Note 7. Employee Benefit Plans footnote for additional details)

[3] All amounts are net of tax. Amounts in parentheses indicate debits