Note 5 - Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands		Mar. 31, 2024	Dec. 31, 2023
Assets, Fair Value Disclosure		$ 40,599	$ 40,251
Cash and Cash Equivalents [Member]
Assets, Fair Value Disclosure	[1]	40,580	40,229
Equity Securities [Member]
Assets, Fair Value Disclosure		19	22
Marketable Securities [Member]
Assets, Fair Value Disclosure		19	22
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure		40,599	40,251
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Assets, Fair Value Disclosure	[1]	40,580	40,229
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Assets, Fair Value Disclosure		19	22
Fair Value, Inputs, Level 1 [Member] | Marketable Securities [Member]
Assets, Fair Value Disclosure		19	22
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Assets, Fair Value Disclosure	[1]	0	0
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Marketable Securities [Member]
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Assets, Fair Value Disclosure	[1]	0	0
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Marketable Securities [Member]
Assets, Fair Value Disclosure		$ 0	$ 0

[1] As of March 31, 2024 and December 31, 2023, included investments in money market mutual funds managed or advised by GAMCO Investors, Inc.