Note 12 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Recurring [Member]
Marketable equity securities	$ 767,989	$ 706,954
Marketable equity securities	767,989	706,954
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Marketable equity securities	767,989	706,954
Marketable equity securities	767,989	706,954
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		24,899
Other real estate investments		5,464
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Real estate		0
Other real estate investments		0
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Real estate		0
Other real estate investments		0
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Real estate		24,899
Other real estate investments		$ 5,464