Note 6 - Investments - Gross Unrealized Losses and Related Fair Values of Available for Sale Securities (Details) $ in Thousands	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	194	154
Fair value available-for-sale securities	$ 679,631	$ 660,883
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (12,101)	$ (4,183)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	36	70
Fair value available-for-sale securities	$ 158,852	$ 254,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ (2,056)	$ (4,145)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	230	224
Fair value available-for-sale securities	$ 838,483	$ 915,611
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (14,157)	$ (8,328)
US government and agency securities
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	4	2
Fair value available-for-sale securities	$ 90,591	$ 26,142
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (3,611)	$ (731)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0	2
Fair value available-for-sale securities	$ 0	$ 2,529
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ (2)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	4	4
Fair value available-for-sale securities	$ 90,591	$ 28,671
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (3,611)	$ (733)
State and municipal obligations
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	4	1
Fair value available-for-sale securities	$ 9,626	$ 3,959
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (100)	$ (41)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0	0
Fair value available-for-sale securities	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	4	1
Fair value available-for-sale securities	$ 9,626	$ 3,959
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (100)	$ (41)
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	60	25
Fair value available-for-sale securities	$ 174,848	$ 110,871
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (3,758)	$ (1,728)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0	0
Fair value available-for-sale securities	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	60	25
Fair value available-for-sale securities	$ 174,848	$ 110,871
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (3,758)	$ (1,728)
RMBS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	5	27
Fair value available-for-sale securities	$ 42,003	$ 184,378
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (305)	$ (535)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	2	16
Fair value available-for-sale securities	$ 915	$ 36,192
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ (9)	$ (992)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	7	43
Fair value available-for-sale securities	$ 42,918	$ 220,570
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (314)	$ (1,527)
CMBS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	43	33
Fair value available-for-sale securities	$ 118,345	$ 89,994
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (3,035)	$ (463)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	6	8
Fair value available-for-sale securities	$ 8,312	$ 6,346
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ (266)	$ (147)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	49	41
Fair value available-for-sale securities	$ 126,657	$ 96,340
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (3,301)	$ (610)
Other ABS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	26	32
Fair value available-for-sale securities	$ 70,759	$ 74,733
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (322)	$ (358)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	3	8
Fair value available-for-sale securities	$ 12,119	$ 25,178
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ (110)	$ (214)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	29	40
Fair value available-for-sale securities	$ 82,878	$ 99,911
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (432)	$ (572)
CLO
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	52	34
Fair value available-for-sale securities	$ 173,459	$ 170,806
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ (970)	$ (327)
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	25	36
Fair value available-for-sale securities	$ 137,506	$ 184,483
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ (1,671)	$ (2,790)
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	77	70
Fair value available-for-sale securities	$ 310,965	$ 355,289
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ (2,641)	$ (3,117)