Note 5 - Investments Schedule of Unrealized Losses (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments	$ 0	$ 0	$ 1,000	$ 0
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	269		269		362
Fair value available-for-sale securities	$ 1,029,555		$ 1,029,555		$ 1,566,440
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 10,002		$ 10,002		$ 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	16		16		21
Fair value available-for-sale securities	$ 30,150		$ 30,150		$ 58,451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 814		$ 814		$ 842
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	285		285		383
Fair value available-for-sale securities	$ 1,059,705		$ 1,059,705		$ 1,624,891
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 10,816		$ 10,816		$ 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	8		8		7
Fair value available-for-sale securities	$ 37,926		$ 37,926		$ 73,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 604		$ 604		$ 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	2		2		0
Fair value available-for-sale securities	$ 1,580		$ 1,580		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 10		$ 10		$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	10		10		7
Fair value available-for-sale securities	$ 39,506		$ 39,506		$ 73,160
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 614		$ 614		$ 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	17		17		7
Fair value available-for-sale securities	$ 60,210		$ 60,210		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 439		$ 439		$ 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		0
Fair value available-for-sale securities	$ 0		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0		$ 0		$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	17		17		7
Fair value available-for-sale securities	$ 60,210		$ 60,210		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 439		$ 439		$ 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	108		108		185
Fair value available-for-sale securities	$ 439,016		$ 439,016		$ 788,876
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 5,104		$ 5,104		$ 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	5		5		2
Fair value available-for-sale securities	$ 11,013		$ 11,013		$ 4,582
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 303		$ 303		$ 277
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	113		113		187
Fair value available-for-sale securities	$ 450,029		$ 450,029		$ 793,458
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 5,407		$ 5,407		$ 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	29		29		56
Fair value available-for-sale securities	$ 114,243		$ 114,243		$ 311,031
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,862		$ 1,862		$ 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	5		5		1
Fair value available-for-sale securities	$ 14,262		$ 14,262		$ 1,398
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 315		$ 315		$ 9
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	34		34		57
Fair value available-for-sale securities	$ 128,505		$ 128,505		$ 312,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 2,177		$ 2,177		$ 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	30		30		37
Fair value available-for-sale securities	$ 122,980		$ 122,980		$ 218,170
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,009		$ 1,009		$ 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		3		2
Fair value available-for-sale securities	$ 1,811		$ 1,811		$ 6,585
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 182		$ 182		$ 114
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	33		33		39
Fair value available-for-sale securities	$ 124,791		$ 124,791		$ 224,755
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 1,191		$ 1,191		$ 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	64		64		58
Fair value available-for-sale securities	$ 174,128		$ 174,128		$ 131,268
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 478		$ 478		$ 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	1		1		16
Fair value available-for-sale securities	$ 1,484		$ 1,484		$ 45,886
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 4		$ 4		$ 442
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	65		65		74
Fair value available-for-sale securities	$ 175,612		$ 175,612		$ 177,154
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 482		$ 482		$ 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	2		2		12
Fair value available-for-sale securities	$ 1,196		$ 1,196		$ 13,034
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 6		$ 6		$ 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		0
Fair value available-for-sale securities	$ 0		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0		$ 0		$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	2		2		12
Fair value available-for-sale securities	$ 1,196		$ 1,196		$ 13,034
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 6		6		$ 325
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments			500
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments			$ 500
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	11		11
Fair value available-for-sale securities	$ 79,856		$ 79,856
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 500		$ 500
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	11		11
Fair value available-for-sale securities	$ 79,856		$ 79,856
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 500		$ 500