Note 15 - Accumulated Other Comprehensive Income (Loss) - Rollforward of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	$ (23,394)	$ 30,839	(106,286)	$ 143,602
Net realized gains (losses) on disposals and non-credit related impairment losses	3,238	10,884	4,490	24,172
Net decrease (increase) in expected credit losses	0	147	725	(2,051)
Other comprehensive income (loss), net of tax	(26,632)	19,808	(111,501)	121,481
AOCI, Net of Tax, Balance at end of period	152,224		152,224
Other Comprehensive Income
Other Comprehensive Income, before Tax [Abstract]
AOCI before Tax, Balance at beginning of period	226,400	268,558	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	(29,613)	39,037	(134,539)	181,775
Net realized gains (losses) on disposals and non-credit related impairment losses	4,099	13,777	5,684	30,597
Net decrease (increase) in expected credit losses	0	186	918	(2,596)
Other comprehensive income (loss)	(33,712)	25,074	(141,141)	153,774
AOCI before Tax, Balance at end of period	192,688	293,632	192,688	293,632
Other Comprehensive Income, Tax [Abstract]
AOCI, Tax, Balance at beginning of period	47,544	56,397	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	(6,219)	8,198	(28,253)	38,173
Net realized gains (losses) on disposals and non-credit related impairment losses	861	2,893	1,194	6,425
Net decrease (increase) in expected credit losses	0	39	193	(545)
Other comprehensive income (loss)	(7,080)	5,266	(29,640)	32,293
AOCI Tax, Balance at end of period	40,464	61,663	40,464	61,663
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period	178,856	212,161	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	(23,394)	30,839	(106,286)	143,602
Net realized gains (losses) on disposals and non-credit related impairment losses	3,238	10,884	4,490	24,172
Net decrease (increase) in expected credit losses	0	147	725	(2,051)
Other comprehensive income (loss), net of tax	(26,632)	19,808	(111,501)	121,481
AOCI, Net of Tax, Balance at end of period	$ 152,224	$ 231,969	$ 152,224	$ 231,969