Note 3 - Investments (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	483	543
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 450,989	$ 484,679
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	34,303	46,923
Debt Securities, Available-for-Sale, Allowance for Credit Loss	904	236
Proceeds from Sale of Debt Securities, Available-for-Sale	10,100	19,700	$ 17,400
Debt Securities, Available-for-Sale	643,799	515,064
Securities on Deposit With State Regulatory Authorities [Member]
Debt Securities, Available-for-Sale	$ 8,600	$ 8,500