Note 15 - Accumulated Other Comprehensive Income (Loss) - Rollforward of Accumulated Other Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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	(147,369)	$ (72,293)
Net realized gains (losses) on disposals and non-credit related impairment losses	(624)	8,394
Net decrease (increase) in expected credit losses	245	0
Other comprehensive income (loss), net of tax	(146,990)	(80,687)
AOCI, Net of Tax, Balance at end of period	116,735
Other Comprehensive Income
Other Comprehensive Income, before Tax [Abstract]
AOCI before Tax, Balance at beginning of period	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	(186,543)	(91,511)
Net realized gains (losses) on disposals and non-credit related impairment losses	(790)	10,625
Net decrease (increase) in expected credit losses	310
Other comprehensive income (loss)	(186,063)	(102,136)
AOCI before Tax, Balance at end of period	147,766	37,722
Other Comprehensive Income, Tax [Abstract]
AOCI, Tax, Balance at beginning of period	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	(39,174)	(19,218)
Net realized gains (losses) on disposals and non-credit related impairment losses	(166)	2,231
Net decrease (increase) in expected credit losses	65
Other comprehensive income (loss)	(39,073)	(21,449)
AOCI Tax, Balance at end of period	31,031	7,921
Other Comprehensive Income, Net of Tax [Abstract]
AOCI, Net of Tax, Balance at beginning of period	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	(147,369)	(72,293)
Net realized gains (losses) on disposals and non-credit related impairment losses	(624)
Net decrease (increase) in expected credit losses	245	8,394
Other comprehensive income (loss), net of tax	(146,990)	(80,687)
AOCI, Net of Tax, Balance at end of period	$ 116,735	$ 29,801