Note 3 - Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale	$ 662,992	$ 643,799
Equity securities	37,171	43,160
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale	38,342	39,420
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	9,884	9,902
Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-sale	29,105	29,511
Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-sale	319,755	300,239
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale	265,906	264,727
Fair Value, Recurring [Member]
Equity securities	37,171	43,160
Cash, cash equivalents, and restricted cash	61,764	51,852
Total assets	761,927	738,811
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale	38,342	39,420
Fair Value, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	9,884	9,902
Fair Value, Recurring [Member] | Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-sale	29,105	29,511
Fair Value, Recurring [Member] | Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-sale	319,755	300,239
Fair Value, Recurring [Member] | Asset-Backed Securities [Member]
Debt Securities, Available-for-sale	265,906	264,727
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Equity securities	37,171	43,160
Cash, cash equivalents, and restricted cash	61,764	51,852
Total assets	98,935	95,012
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-Backed Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Equity securities	0	0
Cash, cash equivalents, and restricted cash	0	0
Total assets	662,992	643,799
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale	38,342	39,420
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	9,884	9,902
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-sale	29,105	29,511
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-sale	319,755	300,239
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-Backed Securities [Member]
Debt Securities, Available-for-sale	265,906	264,727
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Equity securities	0	0
Cash, cash equivalents, and restricted cash	0	0
Total assets	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Special Revenue Excluding Asset Backed Securities [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities and Other Debt Obligations [Member]
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-Backed Securities [Member]
Debt Securities, Available-for-sale	$ 0	$ 0