11. Segment Information Segment Profit Reconciliations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	$ 1,245,945	$ 769,601	$ 2,144,644	$ 1,896,867
Marketable Securities, Unrealized Gain (Loss)	1,183,488	716,389	2,011,159	1,775,619
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	49,200	53,300	121,500	106,900
Corporate, Non-Segment [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income before income taxes	(3,200)	(2,800)	(6,900)	(5,700)
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Marketable Securities, Unrealized Gain (Loss)	1,183,500	716,400	2,011,200	1,775,600
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	(800)	(1,200)	(1,700)	(2,500)
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	$ 17,200	$ 3,900	$ 20,500	$ 22,600