Note 5 - Investments Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	232	232	154
Fair Value, Less Than 12 Months	$ 729,300	$ 729,300	$ 660,883
Unrealized Losses, Less Than 12 Months	$ (22,118)	$ (22,118)	$ (4,183)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	34	34	70
Fair Value, 12 Months or Greater	$ 146,401	$ 146,401	$ 254,728
Unrealized Losses, 12 Months or Greater	$ (5,791)	$ (5,791)	$ (4,145)
Continuous Loss Position, Total
Number of Securities, Total | security	266	266	224
Fair Value, Total	$ 875,701	$ 875,701	$ 915,611
Unrealized Losses, Total	(27,909)	(27,909)	$ (8,328)
Other-than-temporary impairment losses	$ (3,600)	$ (4,200)
US government and agency securities
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security			2
Fair Value, Less Than 12 Months			$ 26,142
Unrealized Losses, Less Than 12 Months			$ (731)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security			2
Fair Value, 12 Months or Greater			$ 2,529
Unrealized Losses, 12 Months or Greater			$ (2)
Continuous Loss Position, Total
Number of Securities, Total | security			4
Fair Value, Total			$ 28,671
Unrealized Losses, Total			$ (733)
State and municipal obligations
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	3	3	1
Fair Value, Less Than 12 Months	$ 8,540	$ 8,540	$ 3,959
Unrealized Losses, Less Than 12 Months	$ (91)	$ (91)	$ (41)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	0	0	0
Fair Value, 12 Months or Greater	$ 0	$ 0	$ 0
Unrealized Losses, 12 Months or Greater	$ 0	$ 0	$ 0
Continuous Loss Position, Total
Number of Securities, Total | security	3	3	1
Fair Value, Total	$ 8,540	$ 8,540	$ 3,959
Unrealized Losses, Total	$ (91)	$ (91)	$ (41)
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	56	56	25
Fair Value, Less Than 12 Months	$ 181,498	$ 181,498	$ 110,871
Unrealized Losses, Less Than 12 Months	$ (3,572)	$ (3,572)	$ (1,728)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	0	0	0
Fair Value, 12 Months or Greater	$ 0	$ 0	$ 0
Unrealized Losses, 12 Months or Greater	$ 0	$ 0	$ 0
Continuous Loss Position, Total
Number of Securities, Total | security	56	56	25
Fair Value, Total	$ 181,498	$ 181,498	$ 110,871
Unrealized Losses, Total	$ (3,572)	$ (3,572)	$ (1,728)
RMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	2	2	27
Fair Value, Less Than 12 Months	$ 3,776	$ 3,776	$ 184,378
Unrealized Losses, Less Than 12 Months	$ (2)	$ (2)	$ (535)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	3	3	16
Fair Value, 12 Months or Greater	$ 10,220	$ 10,220	$ 36,192
Unrealized Losses, 12 Months or Greater	$ (80)	$ (80)	$ (992)
Continuous Loss Position, Total
Number of Securities, Total | security	5	5	43
Fair Value, Total	$ 13,996	$ 13,996	$ 220,570
Unrealized Losses, Total	$ (82)	$ (82)	$ (1,527)
CMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	47	47	36
Fair Value, Less Than 12 Months	$ 130,339	$ 130,339	$ 109,589
Unrealized Losses, Less Than 12 Months	$ (8,353)	$ (8,353)	$ (478)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	5	5	8
Fair Value, 12 Months or Greater	$ 6,965	$ 6,965	$ 6,346
Unrealized Losses, 12 Months or Greater	$ (312)	$ (312)	$ (147)
Continuous Loss Position, Total
Number of Securities, Total | security	52	52	44
Fair Value, Total	$ 137,304	$ 137,304	$ 115,935
Unrealized Losses, Total	$ (8,665)	$ (8,665)	$ (625)
Other ABS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	124	124	63
Fair Value, Less Than 12 Months	$ 405,147	$ 405,147	$ 225,944
Unrealized Losses, Less Than 12 Months	$ (10,100)	$ (10,100)	$ (670)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	26	26	44
Fair Value, 12 Months or Greater	$ 129,216	$ 129,216	$ 209,661
Unrealized Losses, 12 Months or Greater	$ (5,399)	$ (5,399)	$ (3,004)
Continuous Loss Position, Total
Number of Securities, Total | security	150	150	107
Fair Value, Total	$ 534,363	$ 534,363	$ 435,605
Unrealized Losses, Total	$ (15,499)	$ (15,499)	$ (3,674)