Note 6 - Investments Gross Unrealized Losses and Related Fair Values of Available for Sale Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	154	550
Fair value available-for-sale securities	$ 660,883	$ 2,201,228
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 4,183	$ 50,707
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	70	237
Fair value available-for-sale securities	$ 254,728	$ 957,742
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 4,145	$ 37,333
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	224	787
Fair value available-for-sale securities	$ 915,611	$ 3,158,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	8,328	88,040
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	1,700	$ 1,400
Other Than Temporary Impairment Losses, Investments, Credit Losses, Portion Recognized in AOCI	$ 0	$ 0	$ 0
US government and agency securities
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	2	2
Fair value available-for-sale securities	$ 26,142	$ 27,415
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 731	$ 796
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	2	8
Fair value available-for-sale securities	$ 2,529	$ 23,476
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 2	$ 712
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	4	10
Fair value available-for-sale securities	$ 28,671	$ 50,891
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 733	$ 1,508
State and municipal obligations
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	1	12
Fair value available-for-sale securities	$ 3,959	$ 41,263
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 41	$ 955
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0	16
Fair value available-for-sale securities	$ 0	$ 39,982
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ 945
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	1	28
Fair value available-for-sale securities	$ 3,959	$ 81,245
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 41	$ 1,900
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	25	330
Fair value available-for-sale securities	$ 110,871	$ 1,208,430
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 1,728	$ 36,284
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0	126
Fair value available-for-sale securities	$ 0	$ 601,533
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ 27,604
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	25	456
Fair value available-for-sale securities	$ 110,871	$ 1,809,963
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 1,728	$ 63,888
RMBS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	27	15
Fair value available-for-sale securities	$ 184,378	$ 92,315
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 535	$ 782
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	16	28
Fair value available-for-sale securities	$ 36,192	$ 77,395
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 992	$ 3,704
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	43	43
Fair value available-for-sale securities	$ 220,570	$ 169,710
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 1,527	$ 4,486
CMBS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	36	62
Fair value available-for-sale securities	$ 109,589	$ 328,696
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 478	$ 3,973
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	8	33
Fair value available-for-sale securities	$ 6,346	$ 125,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 147	$ 3,385
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	44	95
Fair value available-for-sale securities	$ 115,935	$ 454,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 625	$ 7,358
Other ABS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	63	129
Fair value available-for-sale securities	$ 225,944	$ 503,109
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 670	$ 7,917
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	44	26
Fair value available-for-sale securities	$ 209,661	$ 89,628
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 3,004	$ 983
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	107	155
Fair value available-for-sale securities	$ 435,605	$ 592,737
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 3,674	$ 8,900