Note 15 - Accumulated Other Comprehensive Income (Loss) - Rollforward of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period			$ 263,725
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	$ 64,477	$ 185,056	(82,892)	$ 112,763
Net realized gains (losses) on disposals and non-credit related impairment losses	1,876	4,894	1,252	13,288
Net decrease (increase) in expected credit losses	480	(2,198)	725	(2,198)
Other comprehensive income (loss), net of tax	62,121	182,360	(84,869)	101,673
AOCI, Net of Tax, Balance at end of period	178,856		178,856
Other Comprehensive Income
Other Comprehensive Income, before Tax [Abstract]
AOCI before Tax, Balance at beginning of period	147,766	37,722	333,829	139,858
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	81,617	234,249	(104,926)	142,738
Net realized gains (losses) on disposals and non-credit related impairment losses	2,375	6,195	1,585	16,820
Net decrease (increase) in expected credit losses	608	(2,782)	918	(2,782)
Other comprehensive income (loss)	78,634	230,836	(107,429)	128,700
AOCI before Tax, Balance at end of period	226,400	268,558	226,400	268,558
Other Comprehensive Income, Tax [Abstract]
AOCI, Tax, Balance at beginning of period	31,031	7,921	70,104	29,370
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	17,140	49,193	(22,034)	29,975
Net realized gains (losses) on disposals and non-credit related impairment losses	499	1,301	333	3,532
Net decrease (increase) in expected credit losses	128	(584)	193	(584)
Other comprehensive income (loss)	16,513	48,476	(22,560)	27,027
AOCI Tax, Balance at end of period	47,544	56,397	47,544	56,397
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period	116,735	29,801	263,725	110,488
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	64,477	185,056	(82,892)	112,763
Net realized gains (losses) on disposals and non-credit related impairment losses	1,876	4,894	1,252	13,288
Net decrease (increase) in expected credit losses	480	(2,198)	725	(2,198)
Other comprehensive income (loss), net of tax	62,121	182,360	(84,869)	101,673
AOCI, Net of Tax, Balance at end of period	$ 178,856	$ 212,161	$ 178,856	$ 212,161