Other Comprehensive Income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and postretirement benefits [Abstract]
Amortization of net actuarial loss, Gross Amount	[1]	$ 3,760	$ 4,763	$ 6,963
Amortization of net actuarial loss, Income Tax (Provision) Benefit	[1]	(1,417)	(1,825)	(2,667)
Amortization of net actuarial loss, Net Amount	[1]	2,343	2,938	4,296
Actuarial gains (losses), Gross Amount	[1]	25,776	(15,013)	19,482
Actuarial gains (losses), Income Tax (Provision) Benefit	[1]	(9,371)	5,754	(7,456)
Actuarial gains (losses), Net Amount	[1]	16,405	(9,259)	12,026
Foreign currency translation adjustments, Gross Amount		(146)	0	29
Foreign currency translation adjustments, Income Tax (Provision) Benefit		0	0	0
Foreign currency translation adjustments, Net Amount		(146)	0	29
Total other comprehensive income, Gross Amount		29,390	(10,250)	26,474
Total other comprehensive income, Income Tax (Provision) Benefit		(10,788)	3,929	(10,123)
Total other comprehensive income (loss), net of taxes		$ 18,602	$ (6,321)	$ 16,351

[1] Actuarial gains (losses) are amortized into costs of sales and operating expenses or selling, general and administrative expenses as appropriate. (See Note 10 - Retirement Plans).