2. Short-Term Investments (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Cost	$ 101,038	$ 37,032
Gross unrealized gain	524	45
Gross unrealized loss	(146)	(423)
Fair value	101,416	36,654
Trading securities - Debt [Member]
Cost	90,061	33,643
Gross unrealized gain	425	18
Gross unrealized loss	(4)	(19)
Fair value	90,482	33,642
Trading securities - Equity [Member]
Cost	10,977	3,389
Gross unrealized gain	99	27
Gross unrealized loss	(142)	(404)
Fair value	$ 10,934	$ 3,012