Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (6,791)
Other comprehensive income (loss)	(19,855)	$ (30,704)	$ 120,366
Ending Balance	(26,646)	(6,791)
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change for adoption of ASU			0
Pension and Other Post-Retirement Actuarial Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(58,291)	(69,041)	(64,496)
Other comprehensive income before reclassifications	(21,473)	5,617	(15,671)
Tax effect	5,219	(1,032)	4,373
Other comprehensive income before reclassifications, net of tax	(16,254)	4,585	(11,298)
Amounts reclassified out of AOCI	8,694	8,343	9,147
Tax effect	(2,169)	(2,178)	(2,394)
Amounts reclassified out of AOCI, net of tax	6,525	6,165	6,753
Other comprehensive income (loss)	(9,729)	10,750	(4,545)
Ending Balance	(68,020)	(58,291)	(69,041)
Pension and Other Post-Retirement Actuarial Items [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change for adoption of ASU			0
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	51,500	92,954	(31,266)
Other comprehensive income before reclassifications	(10,126)	(41,454)	124,220
Tax effect	0	0	0
Other comprehensive income before reclassifications, net of tax	(10,126)	(41,454)	124,220
Amounts reclassified out of AOCI	0	0	0
Tax effect	0	0	0
Amounts reclassified out of AOCI, net of tax	0	0	0
Other comprehensive income (loss)	(10,126)	(41,454)	124,220
Ending Balance	41,374	51,500	92,954
Currency Translation Adjustment [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change for adoption of ASU			0
Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	0	1,801	1,110
Other comprehensive income before reclassifications	0	0	1,881
Tax effect	0	0	(659)
Other comprehensive income before reclassifications, net of tax	0	0	1,222
Amounts reclassified out of AOCI	0	0	(817)
Tax effect	0	0	286
Amounts reclassified out of AOCI, net of tax	0	0	(531)
Other comprehensive income (loss)	0	0	691
Ending Balance	0	0	1,801
Unrealized Gain (Loss) on Available-for-Sale Securities [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change for adoption of ASU			(1,801)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(6,791)	25,714	(94,652)
Other comprehensive income before reclassifications	(31,599)	(35,837)	110,430
Tax effect	5,219	(1,032)	3,714
Other comprehensive income before reclassifications, net of tax	(26,380)	(36,869)	114,144
Amounts reclassified out of AOCI	8,694	8,343	8,330
Tax effect	(2,169)	(2,178)	(2,108)
Amounts reclassified out of AOCI, net of tax	6,525	6,165	6,222
Other comprehensive income (loss)	(19,855)	(30,704)	120,366
Ending Balance	$ (26,646)	$ (6,791)	25,714
Accumulated Other Comprehensive Income (Loss) [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change for adoption of ASU			$ (1,801)