Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current year activity:
Accumulated other comprehensive loss	$ (58,234)	$ (102,937)	$ (86,181)	$ (80,705)
Other comprehensive income (loss) before reclassifications	10,477	(8,370)	(14,714)
Amounts reclassified from accumulated other comprehensive income	46,854	5,705	4,832
Other comprehensive income (loss) before tax	57,331	(2,665)	(9,882)
Deferred taxes on current period activity	12,628	14,091	(4,406)
Other comprehensive income (loss) after tax	44,703	(16,756)	(5,476)
Gains and Losses On Cash Flow Hedges
Current year activity:
Accumulated other comprehensive loss	901	763	1,837	1,579
Other comprehensive income (loss) before reclassifications	(435)	(1,643)	(377)
Amounts reclassified from accumulated other comprehensive income	(99)	840	784
Other comprehensive income (loss) before tax	(534)	(803)	407
Deferred taxes on current period activity	(672)	271	149
Other comprehensive income (loss) after tax	138	(1,074)	258
Pension and Post- Employment Benefits
Current year activity:
Accumulated other comprehensive loss	(54,543)	(99,592)	(82,358)	(76,796)
Other comprehensive income (loss) before reclassifications	11,396	(8,279)	(14,165)
Amounts reclassified from accumulated other comprehensive income	46,953	4,865	4,048
Other comprehensive income (loss) before tax	58,349	(3,414)	(10,117)
Deferred taxes on current period activity	13,300	13,820	(4,555)
Other comprehensive income (loss) after tax	45,049	(17,234)	(5,562)
Foreign Currency Translation
Current year activity:
Accumulated other comprehensive loss	(4,592)	(4,108)	(5,660)	(5,488)
Other comprehensive income (loss) before reclassifications	(484)	1,552	(172)
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive income (loss) before tax	(484)	1,552	(172)
Deferred taxes on current period activity	0	0	0
Other comprehensive income (loss) after tax	(484)	1,552	(172)
Foreign Currency | Gains and Losses On Cash Flow Hedges
Current year activity:
Accumulated other comprehensive loss	1,263	959	1,837	1,579
Other comprehensive income (loss) before reclassifications	(333)	(1,180)	(377)
Amounts reclassified from accumulated other comprehensive income	10	632	784
Other comprehensive income (loss) before tax	(323)	(548)	407
Deferred taxes on current period activity	(627)	330	149
Other comprehensive income (loss) after tax	304	(878)	258
Precious Metals | Gains and Losses On Cash Flow Hedges
Current year activity:
Accumulated other comprehensive loss	79	(196)	0	0
Other comprehensive income (loss) before reclassifications	467	(463)	0
Amounts reclassified from accumulated other comprehensive income	(109)	208	0
Other comprehensive income (loss) before tax	358	(255)	0
Deferred taxes on current period activity	83	(59)	0
Other comprehensive income (loss) after tax	275	(196)	0
Copper Swap [Member] | Gains and Losses On Cash Flow Hedges
Current year activity:
Accumulated other comprehensive loss	(441)	0	0	$ 0
Other comprehensive income (loss) before reclassifications	(569)	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive income (loss) before tax	(569)	0	0
Deferred taxes on current period activity	(128)	0	0
Other comprehensive income (loss) after tax	$ (441)	$ 0	$ 0