Note 6 - Investments Schedule of Unrealized Losses (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2013 USD ($)
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	305	62
Fair value available-for-sale securities	$ 1,462,577,000	$ 144,626,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 32,079,000	$ 2,379,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	23	2
Fair value available-for-sale securities	$ 54,203,000	$ 4,482,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 2,221,000	$ 154,000
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	328	64
Fair value available-for-sale securities	$ 1,516,780,000	$ 149,108,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	34,300,000	2,533,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	$ 0	$ 0	$ 0
US government and agency securities
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	1	0
Fair value available-for-sale securities	$ 5,752,000	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 21,000	$ 0
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security		1
Fair value available-for-sale securities	$ 0	$ 3,455,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0	$ 6,000
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	1	1
Fair value available-for-sale securities	$ 5,752,000	$ 3,455,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 21,000	$ 6,000
State and municipal obligations
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	2
Fair value available-for-sale securities	$ 11,674,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 120,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0
Fair value available-for-sale securities	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	2
Fair value available-for-sale securities	$ 11,674,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 120,000
Corporate bonds and notes
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	117	24
Fair value available-for-sale securities	$ 510,807,000	$ 40,917,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 16,773,000	$ 410,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	6	1
Fair value available-for-sale securities	$ 8,700,000	$ 1,027,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 518,000	$ 148,000
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	123	25
Fair value available-for-sale securities	$ 519,507,000	$ 41,944,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 17,291,000	$ 558,000
Residential Mortgage Backed Securities [Member]
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	12
Fair value available-for-sale securities	$ 168,415,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 2,464,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0
Fair value available-for-sale securities	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	12
Fair value available-for-sale securities	$ 168,415,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 2,464,000
CMBS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	58
Fair value available-for-sale securities	$ 387,268,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 8,939,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0
Fair value available-for-sale securities	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	58
Fair value available-for-sale securities	$ 387,268,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 8,939,000
Other ABS
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	96	34
Fair value available-for-sale securities	$ 284,998,000	$ 97,356,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 2,559,000	$ 1,727,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	14	0
Fair value available-for-sale securities	$ 43,225,000	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 1,415,000	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	110	34
Fair value available-for-sale securities	$ 328,223,000	$ 97,356,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 3,974,000	$ 1,727,000
Foreign government securities
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	18	4
Fair value available-for-sale securities	$ 18,733,000	$ 6,353,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 1,095,000	$ 242,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	3	0
Fair value available-for-sale securities	$ 2,278,000	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 288,000	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	21	4
Fair value available-for-sale securities	$ 21,011,000	$ 6,353,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 1,383,000	$ 242,000
Equity securities
Continuous Loss Position Less Than Twelve Months
Number of Securities | security	1
Fair value available-for-sale securities	$ 74,930,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 108,000
Continuous Unrealized Loss Position, Twelve Months Or Greater
Number of securities | security	0
Fair value available-for-sale securities	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	$ 0
Continuous Loss Position, Total
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	1
Fair value available-for-sale securities	$ 74,930,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 108,000