Note 6 - Investments - Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	411	194
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 1,644,089	$ 679,631
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (23,471)	$ (12,101)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	65	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 184,506	$ 158,852
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (10,551)	$ (2,056)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	476	230
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 1,828,595	$ 838,483
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (34,022)	$ (14,157)
U.S. government and agencies securities
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	14	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 175,339	$ 90,591
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (1,207)	$ (3,611)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	2	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 9,477	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (677)	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	16	4
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 184,816	$ 90,591
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1,884)	$ (3,611)
State and municipal obligations
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	15	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 20,223	$ 9,626
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (254)	$ (100)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 2,831	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (103)	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	16	4
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 23,054	$ 9,626
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (357)	$ (100)
Corporate bonds and notes
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	175	60
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 719,649	$ 174,848
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (16,424)	$ (3,758)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	32	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 90,207	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (8,557)	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	207	60
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 809,856	$ 174,848
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (24,981)	$ (3,758)
RMBS
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	36	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 258,829	$ 42,003
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (3,291)	$ (305)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	2	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 758	$ 915
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (9)	$ (9)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	38	7
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 259,587	$ 42,918
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (3,300)	$ (314)
CMBS
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	59	43
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 118,990	$ 118,345
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (1,555)	$ (3,035)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	12	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 25,224	$ 8,312
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (926)	$ (266)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	71	49
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 144,214	$ 126,657
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (2,481)	$ (3,301)
CLO
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	68	52
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 251,734	$ 173,459
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (287)	$ (970)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	14	25
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 55,150	$ 137,506
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (256)	$ (1,671)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	82	77
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 306,884	$ 310,965
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (543)	$ (2,641)
Other ABS
Continuous Loss Position, Total
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | security	44	26
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 99,325	$ 70,759
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (453)	$ (322)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | security	2	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 859	$ 12,119
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (23)	$ (110)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	46	29
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 100,184	$ 82,878
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (476)	$ (432)