Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Marketable Securities, Gain (Loss), Total	$ 61,085	$ (4,667)
Payment, Tax Withholding, Share-based Payment Arrangement	9,082	5,149
Proceeds from Change in Tenants' Security Deposits	650	70
Increase (Decrease) in Other Operating Assets, Total	$ 34,936	29,454
Revision of Prior Period, Reclassification, Adjustment [Member]
Marketable Securities, Gain (Loss), Total		4,700
Proceeds from (Payments for) Other Financing Activities		(5,100)
Payment, Tax Withholding, Share-based Payment Arrangement		5,100
Proceeds from Change in Tenants' Security Deposits		100
Increase (Decrease) in Other Operating Assets, Total		(4,700)
Other Income		$ (4,700)