Note 6 - Marketable Securities (Details Textual) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Marketable Securities, Gain (Loss), Total	$ 24,297	$ 526,243	$ 85,382	$ 521,577

Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

No definition available.

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration