Note 11 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Recurring [Member]
Marketable equity securities	$ 556,791	$ 9,353
Marketable equity securities	556,791	9,353
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Marketable equity securities	556,791	9,353
Marketable equity securities	556,791	9,353
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Marketable equity securities	0
Marketable equity securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Marketable equity securities		0
Marketable equity securities		0
Fair Value, Nonrecurring [Member]
Real estate	5,300	39,510
Other real estate investments		32,974
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Real estate	0	0
Other real estate investments		0
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Real estate	0	0
Other real estate investments		0
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Real estate	$ 5,300	39,510
Other real estate investments		$ 32,974