Note 5 - Investments Schedule of Unrealized Losses (Details) $ in Thousands	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	335	362
Fair value available-for-sale securities	$ 1,309,877	$ 1,566,440
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 29,214	$ 37,941
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	13	21
Fair value available-for-sale securities	$ 43,681	$ 58,451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 600	$ 842
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	348	383
Fair value available-for-sale securities	$ 1,353,558	$ 1,624,891
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 29,814	$ 38,783
US government and agency securities
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	9	7
Fair value available-for-sale securities	$ 74,457	$ 73,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 3,160	$ 3,459
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	0	0
Fair value available-for-sale securities	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	9	7
Fair value available-for-sale securities	$ 74,457	$ 73,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 3,160	$ 3,459
US States and Political Subdivisions Debt Securities [Member]
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	5	7
Fair value available-for-sale securities	$ 19,981	$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 632	$ 821
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	0	0
Fair value available-for-sale securities	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	5	7
Fair value available-for-sale securities	$ 19,981	$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 632	$ 821
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	150	185
Fair value available-for-sale securities	$ 620,609	$ 788,876
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 16,360	$ 22,135
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	2	2
Fair value available-for-sale securities	$ 4,471	$ 4,582
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 336	$ 277
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	152	187
Fair value available-for-sale securities	$ 625,080	$ 793,458
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 16,696	$ 22,412
RMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	54	56
Fair value available-for-sale securities	$ 217,577	$ 311,031
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 5,541	$ 7,822
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	3	1
Fair value available-for-sale securities	$ 7,308	$ 1,398
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 65	$ 9
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	57	57
Fair value available-for-sale securities	$ 224,885	$ 312,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 5,606	$ 7,831
CMBS
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	38	37
Fair value available-for-sale securities	$ 186,354	$ 218,170
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 2,519	$ 2,909
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	3	2
Fair value available-for-sale securities	$ 9,924	$ 6,585
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 51	$ 114
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	41	39
Fair value available-for-sale securities	$ 196,278	$ 224,755
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 2,570	$ 3,023
Other ABS
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	75	58
Fair value available-for-sale securities	$ 186,578	$ 131,268
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 949	$ 470
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	5	16
Fair value available-for-sale securities	$ 21,978	$ 45,886
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 148	$ 442
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	80	74
Fair value available-for-sale securities	$ 208,556	$ 177,154
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 1,097	$ 912
Foreign government securities
Continuous Loss Position Less Than Twelve Months [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	4	12
Fair value available-for-sale securities	$ 4,321	$ 13,034
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 53	$ 325
Continuous Unrealized Loss Position, Twelve Months Or Greater
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	0	0
Fair value available-for-sale securities	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	4	12
Fair value available-for-sale securities	$ 4,321	$ 13,034
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 53	$ 325