Other Results of Operations Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Manufacturing revenues		$ 326,197	$ 412,826	$ 391,920
Losses from managed funds		(8,118)	(69,038)	(37,237)
Asset management fees		28,831	29,492	34,777
Dividend income		(452)	3,856	5,482
Income from associated companies classified as other revenues		75,889	17,184	75,717
Revenues of oil and gas production and development businesses		61,541	49,890	45,939
Gain on sale of subsidiaries		179,605	0	0
Other		86,384	43,976	32,630
Total other income		748,508	488,186	549,228
Taxes other than income or payroll		39,600	35,400	21,900
Advertising costs		21,600	$ 20,000	$ 18,100
Disposed of by Sale | Conwed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of subsidiaries	$ 179,900	$ 178,236