11. Segment Information Segment Profit Reconciliations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	$ (335,216)	$ 350,131	$ 1,561,651	$ 1,553,906
Marketable Securities, Unrealized Gain (Loss)	(390,620)	318,007	1,384,999	1,420,339
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	55,000	32,700	161,900	112,600
Corporate, Non-Segment [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	(3,100)	(2,500)	(8,800)	(6,700)
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Marketable Securities, Unrealized Gain (Loss)	(390,600)	318,000	1,385,000	1,420,300
Foreign Currency Gain (Loss) [Member] | Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	(900)	(700)	(3,400)	(1,900)
Other Nonoperating Income (Expense) [Member] | Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	$ 4,400	$ 2,600	$ 27,000	$ 29,600