Note 15 - Accumulated Other Comprehensive Income (Loss) - Rollforward of Accumulated Other Comprehensive Income (Loss) - Level 4 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance at beginning of period, net of tax	$ 110,488
Unrealized holding gains (losses) arising during the period for which an allowance for expected losses has not been recognized	178,761	$ 180,441	$ (97,356)
Net realized gains (losses) on disposals and non-credit related impairment losses	26,440	8,897	(10,270)
Net decrease (increase) in expected credit losses	(991)	0	0
Net unrealized gains (losses) on investments, net of tax	153,312	171,544	(87,086)
Other adjustments to comprehensive income, net	(75)	(136)	133
Other comprehensive income (loss), net of tax	153,237	171,408	(86,953)
Balance at end of period, net of tax	263,725	110,488
Other Comprehensive Income (Loss)
Other Comprehensive Income (Loss), before Tax [Abstract]
Balance at beginning of period, before tax	139,858	(77,114)	32,669
Cumulative effect of adopting the accounting standard update, before tax			284
Balance adjusted for cumulative effect of adopting accounting standard updates, before tax			32,953
Unrealized holding gains (losses) arising during the period, before tax	226,280	228,406	(123,235)
Net realized gains (losses) on disposals and non-credit related impairment losses, before Tax	33,468	11,262	(13,000)
Net decrease (increase) in expected credit losses, before tax	(1,254)
Net unrealized gains (losses) on investments	194,066	217,144	(110,235)
Other Adjustments to Other Comprehensive Income, BeforeTax	(95)	(172)	168
OCI, before tax	193,971	216,972	(110,067)
Balance at end of period, before tax	333,829	139,858	(77,114)
Other Comprehensive Income (Loss), Tax [Abstract]
Balance at beginning of period, tax	29,370	(16,194)	9,584
Cumulative effect of adopting the accounting standard update, tax			(2,664)
Balance adjusted for cumulative effect of adopting accounting standard updates, tax			6,920
Unrealized holding gains (losses) arising during the period, tax	47,519	47,965	(25,879)
Net realized gains (losses) on disposals and non-credit-related impairment losses, tax	7,028	2,365	(2,730)
Net decrease (increase) in expected credit losses, tax	(263)
Net unrealized gains (losses) on investments, tax	40,754	45,600	(23,149)
Other adjustments to comprehensive income, tax	(20)	(36)	35
OCI, tax	40,734	45,564	(23,114)
Balance at end of period, tax	70,104	29,370	(16,194)
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance at beginning of period, net of tax	110,488	(60,920)	23,085
Cumulative effect of adopting the accounting standard update for financial instruments, net of tax			2,948
Balance adjusted for cumulative effect of adopting accounting standard updates, net of tax			26,033
Unrealized holding gains (losses) arising during the period for which an allowance for expected losses has not been recognized	178,761	180,441	(97,356)
Net realized gains (losses) on disposals and non-credit related impairment losses	26,440	8,897	(10,270)
Net decrease (increase) in expected credit losses	(991)
Net unrealized gains (losses) on investments, net of tax	153,312	171,544	(87,086)
Other adjustments to comprehensive income, net	(75)	(136)	133
Other comprehensive income (loss), net of tax	153,237	171,408	(86,953)
Balance at end of period, net of tax	$ 263,725	$ 110,488	$ (60,920)