Note 5 - Investments Gain (Loss) on Investments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Gain (Loss) on Investments [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	335		362
Other gains	$ 18	$ 18
Net realized losses on investments	(8,179)	(5,579)
Unrealized gains on trading securities	5,226	35,231
Total net gains on investments	(2,953)	29,652
Net gains on other financial instruments	102	1,634
Net gains on investments and other financial instruments	(2,851)	31,286
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,309,877		$ 1,566,440
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 29,214		$ 37,941
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	13		21
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 43,681		$ 58,451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 600		$ 842
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	348		383
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,353,558		$ 1,624,891
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	29,814		$ 38,783
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	(2,509)	(3,148)
Equity securities
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	0	(170)
Trading Securities [Member]
Gain (Loss) on Investments [Line Items]
Trading securities	(5,694)	(2,240)
Short-term Investments [Member]
Gain (Loss) on Investments [Line Items]
Short-term investments	6	(39)
Other investments
Gain (Loss) on Investments [Line Items]
Cost-method Investments, Realized Gain (Loss), Excluding Other than Temporary Impairments	$ 0	$ 0
US States and Political Subdivisions Debt Securities [Member]
Gain (Loss) on Investments [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	5		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 19,981		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 632		$ 821
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0		$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	5		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 19,981		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 632		$ 821