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, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	79		79		550
Fair Value, Less Than 12 Months	$ 318,069		$ 318,069		$ 2,201,228
Unrealized Losses, Less Than 12 Months	$ 2,331		$ 2,331		$ 50,707
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	110		110		237
Fair Value, 12 Months or Greater	$ 349,606		$ 349,606		$ 957,742
Unrealized Losses, 12 Months or Greater	$ 4,177		$ 4,177		$ 37,333
Continuous Loss Position, Total
Number of Securities, Total | security	189		189		787
Fair Value, Total	$ 667,675		$ 667,675		$ 3,158,970
Unrealized Losses, Total	$ 6,508		$ 6,508		$ 88,040
US government and agency securities
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	0		0		2
Fair Value, Less Than 12 Months	$ 0		$ 0		$ 27,415
Unrealized Losses, Less Than 12 Months	$ 0		$ 0		$ 796
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	4		4		8
Fair Value, 12 Months or Greater	$ 12,370		$ 12,370		$ 23,476
Unrealized Losses, 12 Months or Greater	$ 36		$ 36		$ 712
Continuous Loss Position, Total
Number of Securities, Total | security	4		4		10
Fair Value, Total	$ 12,370		$ 12,370		$ 50,891
Unrealized Losses, Total	$ 36		$ 36		$ 1,508
State and municipal obligations
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	1		1		12
Fair Value, Less Than 12 Months	$ 3,249		$ 3,249		$ 41,263
Unrealized Losses, Less Than 12 Months	$ 1		$ 1		$ 955
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	1		1		16
Fair Value, 12 Months or Greater	$ 999		$ 999		$ 39,982
Unrealized Losses, 12 Months or Greater	$ 1		$ 1		$ 945
Continuous Loss Position, Total
Number of Securities, Total | security	2		2		28
Fair Value, Total	$ 4,248		$ 4,248		$ 81,245
Unrealized Losses, Total	$ 2		$ 2		$ 1,900
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	19		19		330
Fair Value, Less Than 12 Months	$ 82,685		$ 82,685		$ 1,208,430
Unrealized Losses, Less Than 12 Months	$ 586		$ 586		$ 36,284
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	27		27		126
Fair Value, 12 Months or Greater	$ 102,857		$ 102,857		$ 601,533
Unrealized Losses, 12 Months or Greater	$ 752		$ 752		$ 27,604
Continuous Loss Position, Total
Number of Securities, Total | security	46		46		456
Fair Value, Total	$ 185,542		$ 185,542		$ 1,809,963
Unrealized Losses, Total	$ 1,338		$ 1,338		$ 63,888
RMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	1		1		15
Fair Value, Less Than 12 Months	$ 32		$ 32		$ 92,315
Unrealized Losses, Less Than 12 Months	$ 1		$ 1		$ 782
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	24		24		28
Fair Value, 12 Months or Greater	$ 58,905		$ 58,905		$ 77,395
Unrealized Losses, 12 Months or Greater	$ 1,424		$ 1,424		$ 3,704
Continuous Loss Position, Total
Number of Securities, Total | security	25		25		43
Fair Value, Total	$ 58,937		$ 58,937		$ 169,710
Unrealized Losses, Total	$ 1,425		$ 1,425		$ 4,486
CMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	16		16		62
Fair Value, Less Than 12 Months	$ 33,267		$ 33,267		$ 328,696
Unrealized Losses, Less Than 12 Months	$ 555		$ 555		$ 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	$ 6,751		$ 6,751		$ 125,728
Unrealized Losses, 12 Months or Greater	$ 177		$ 177		$ 3,385
Continuous Loss Position, Total
Number of Securities, Total | security	26		26		95
Fair Value, Total	$ 40,018		$ 40,018		$ 454,424
Unrealized Losses, Total	$ 732		$ 732		$ 7,358
Other ABS
Continuous Loss Position Less Than Twelve Months [Abstract]
Number of Securities, Less than 12 Months | security	42		42		129
Fair Value, Less Than 12 Months	$ 198,836		$ 198,836		$ 503,109
Unrealized Losses, Less Than 12 Months	$ 1,188		$ 1,188		$ 7,917
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of Securities, 12 Months or Greater | security	44		44		26
Fair Value, 12 Months or Greater	$ 167,724		$ 167,724		$ 89,628
Unrealized Losses, 12 Months or Greater	$ 1,787		$ 1,787		$ 983
Continuous Loss Position, Total
Number of Securities, Total | security	86		86		155
Fair Value, Total	$ 366,560		$ 366,560		$ 592,737
Unrealized Losses, Total	2,975		2,975		$ 8,900
OTTI Recognized in Earnings
Continuous Loss Position, Total
Other-than-temporary impairment losses	$ 0	$ 0	0	$ 844
OTTI Recognized in AOCI
Continuous Loss Position, Total
Other-than-temporary impairment losses			$ 0	$ 0