Note 6 - Fair Value Measurements - Assets and Liabilities Carried at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021
Fair value (millions)	$ 1,300	$ 900	$ 1,100	$ 1,400	$ 1,200	$ 2,600	$ 4,700	$ 7,200
Fair Value, Recurring [Member] | Reported Value Measurement [Member]
Cash equivalents	7,913				17,641
Fair value (millions)	1,270				1,200
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents	7,913				17,641
Fair value (millions)	0				0
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents	0				0
Fair value (millions)	0				0
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents	0				0
Fair value (millions)	$ 1,270				$ 1,200