Note 5 - Investments Gain (Loss) on Investments (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
Gain (Loss) on Investments [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security	269		269		362
Other gains	$ 7	$ 15	$ 25	$ 33
Net realized losses on investments	(32)	7,893	(9,393)	3,901
Other than Temporary Impairment Losses, Investments	0	0	(1,000)	0
Unrealized gains on trading securities	2,353	(47)	14,517	62,862
Total net gains on investments	2,321	7,846	4,124	66,763
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	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
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	16		16		21
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 30,150		$ 30,150		$ 58,451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 814		$ 814		$ 842
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	285		285		383
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 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
Net gains (losses) on other financial instruments	159	(135)	836	2,761
Net Gains (Losses) on Investments and Other Financial Instruments	2,480	7,711	4,960	69,524
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	137	5,685	(3,552)	3,703
Equity securities
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	33	0	418	(170)
Trading Securities [Member]
Gain (Loss) on Investments [Line Items]
Trading securities	(223)	1,524	(6,266)	(295)
Short-term Investments [Member]
Gain (Loss) on Investments [Line Items]
Short-term investments	14	38	(18)	(1)
Other investments
Gain (Loss) on Investments [Line Items]
Cost-method Investments, Realized Gain (Loss), Excluding Other than Temporary Impairments	$ 0	$ 631	$ 0	$ 631
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	17		17		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 60,210		$ 60,210		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 439		$ 439		$ 821
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	0		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0		$ 0		$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	17		17		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 60,210		$ 60,210		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 439		$ 439		$ 821