Note 5 - Investments Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) security	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) security	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	115		115		550
Fair Value, Less Than 12 Months	$ 516,478		$ 516,478		$ 2,201,228
Unrealized Losses, Less Than 12 Months	$ 3,013		$ 3,013		$ 50,707
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	80		80		237
Fair Value, 12 Months or Greater	$ 227,267		$ 227,267		$ 957,742
Unrealized Losses, 12 Months or Greater	$ 3,469		$ 3,469		$ 37,333
Continuous Loss Position, Total
Number of Securities, Total | security	195		195		787
Fair Value, Total	$ 743,745		$ 743,745		$ 3,158,970
Unrealized Losses, Total	$ 6,482		$ 6,482		$ 88,040
US government and agency securities
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	4		4		2
Fair Value, Less Than 12 Months	$ 68,719		$ 68,719		$ 27,415
Unrealized Losses, Less Than 12 Months	$ 89		$ 89		$ 796
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	3		3		8
Fair Value, 12 Months or Greater	$ 9,051		$ 9,051		$ 23,476
Unrealized Losses, 12 Months or Greater	$ 17		$ 17		$ 712
Continuous Loss Position, Total
Number of Securities, Total | security	7		7		10
Fair Value, Total	$ 77,770		$ 77,770		$ 50,891
Unrealized Losses, Total	$ 106		$ 106		$ 1,508
State and municipal obligations
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security					12
Fair Value, Less Than 12 Months					$ 41,263
Unrealized Losses, Less Than 12 Months					$ 955
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security					16
Fair Value, 12 Months or Greater					$ 39,982
Unrealized Losses, 12 Months or Greater					$ 945
Continuous Loss Position, Total
Number of Securities, Total | security					28
Fair Value, Total					$ 81,245
Unrealized Losses, Total					$ 1,900
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	28		28		330
Fair Value, Less Than 12 Months	$ 126,732		$ 126,732		$ 1,208,430
Unrealized Losses, Less Than 12 Months	$ 1,145		$ 1,145		$ 36,284
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	4		4		126
Fair Value, 12 Months or Greater	$ 8,543		$ 8,543		$ 601,533
Unrealized Losses, 12 Months or Greater	$ 19		$ 19		$ 27,604
Continuous Loss Position, Total
Number of Securities, Total | security	32		32		456
Fair Value, Total	$ 135,275		$ 135,275		$ 1,809,963
Unrealized Losses, Total	$ 1,164		$ 1,164		$ 63,888
RMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	5		5		15
Fair Value, Less Than 12 Months	$ 30,478		$ 30,478		$ 92,315
Unrealized Losses, Less Than 12 Months	$ 52		$ 52		$ 782
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	23		23		28
Fair Value, 12 Months or Greater	$ 44,649		$ 44,649		$ 77,395
Unrealized Losses, 12 Months or Greater	$ 986		$ 986		$ 3,704
Continuous Loss Position, Total
Number of Securities, Total | security	28		28		43
Fair Value, Total	$ 75,127		$ 75,127		$ 169,710
Unrealized Losses, Total	$ 1,038		$ 1,038		$ 4,486
CMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	18		18		62
Fair Value, Less Than 12 Months	$ 32,861		$ 32,861		$ 328,696
Unrealized Losses, Less Than 12 Months	$ 724		$ 724		$ 3,973
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	10		10		33
Fair Value, 12 Months or Greater	$ 9,120		$ 9,120		$ 125,728
Unrealized Losses, 12 Months or Greater	$ 188		$ 188		$ 3,385
Continuous Loss Position, Total
Number of Securities, Total | security	28		28		95
Fair Value, Total	$ 41,981		$ 41,981		$ 454,424
Unrealized Losses, Total	$ 912		$ 912		$ 7,358
Other ABS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	60		60		129
Fair Value, Less Than 12 Months	$ 257,688		$ 257,688		$ 503,109
Unrealized Losses, Less Than 12 Months	$ 1,003		$ 1,003		$ 7,917
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	40		40		26
Fair Value, 12 Months or Greater	$ 155,904		$ 155,904		$ 89,628
Unrealized Losses, 12 Months or Greater	$ 2,259		$ 2,259		$ 983
Continuous Loss Position, Total
Number of Securities, Total | security	100		100		155
Fair Value, Total	$ 413,592		$ 413,592		$ 592,737
Unrealized Losses, Total	3,262		3,262		$ 8,900
OTTI Recognized in Earnings
Continuous Loss Position, Total
Other-than-temporary impairment losses	$ 0	$ 900	0	$ 1,744
OTTI Recognized in AOCI
Continuous Loss Position, Total
Other-than-temporary impairment losses			$ 0	$ 0