Note 15 - Accumulated Other Comprehensive Income (Loss) - Rollforward of Accumulated Other Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Comprehensive Income, before Tax [Abstract]
Unrealized foreign currency translation adjustments		$ 0		$ (4)
Other Comprehensive Income, Tax [Abstract]
Unrealized foreign currency translation adjustments		0		(1)
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period			$ 110,488
Unrealized holding gains (losses) arising during the period for which an allowance for expected credit losses has not been recognized	$ 30,839	40,654	143,602	190,677
Net realized gains (losses) on disposals and non-credit related impairment losses	10,884	3,477	24,172	4,115
Net decrease (increase) in expected credit losses	147	0	(2,051)	0
Unrealized foreign currency translation adjustments	0	0	0	(3)
Other comprehensive income (loss), net of tax	19,808	37,177	121,481	186,559
AOCI, Net of Tax, Balance at end of period	231,969		231,969
Other Comprehensive Income
Other Comprehensive Income, before Tax [Abstract]
AOCI before Tax, Balance at beginning of period	268,558	111,977	139,858	(77,114)
Unrealized holding gains (losses) arising during the period for which an allowance for expected credit losses has not been recognized	39,037	51,460	181,775	241,363
Net realized gains (losses) on disposals and non-credit related impairment losses	13,777		30,597
Net decrease (increase) in expected credit losses	186	4,401	(2,596)	5,209
Net unrealized gains (losses) on investments	25,074	47,059	153,774	236,154
Other comprehensive income (loss)	25,074	47,059	153,774	236,150
AOCI before Tax, Balance at end of period	293,632	159,036	293,632	159,036
Other Comprehensive Income, Tax [Abstract]
AOCI, Tax, Balance at beginning of period	56,397	23,515	29,370	(16,194)
Unrealized holding gains (losses) arising during the period for which an allowance for expected credit losses has not been recognized	8,198	10,806	38,173	50,686
Net realized gains (losses) on disposals and non-credit related impairment losses	2,893		6,425
Net decrease (increase) in expected credit losses	39	924	(545)	1,094
Net unrealized gains (losses) on investments	5,266	9,882	32,293	49,592
Other comprehensive income (loss)	5,266	9,882	32,293	49,591
AOCI Tax, Balance at end of period	61,663	33,397	61,663	33,397
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period	212,161	88,462	110,488	(60,920)
Unrealized holding gains (losses) arising during the period for which an allowance for expected credit losses has not been recognized	30,839	40,654	143,602	190,677
Net realized gains (losses) on disposals and non-credit related impairment losses	10,884		24,172
Net decrease (increase) in expected credit losses	147	3,477	(2,051)	4,115
Net unrealized gains (losses) on investments	19,808	37,177	121,481	186,562
Other comprehensive income (loss), net of tax	19,808	37,177	121,481	186,559
AOCI, Net of Tax, Balance at end of period	$ 231,969	$ 125,639	$ 231,969	$ 125,639