Note 5 - Investments Gain (Loss) on Investments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($)	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	311		311		362
Other gains	$ 0	$ 0	$ 18	$ 18
Net realized losses on investments	(1,182)	1,587	(9,361)	(3,992)
Other than Temporary Impairment Losses, Investments	(1,000)	0	(1,000)	0
Unrealized gains on trading securities	6,938	27,678	12,164	62,909
Total net gains on investments	4,756	29,265	1,803	58,917
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,139,971		1,139,971		$ 1,566,440
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 13,490		$ 13,490		$ 37,941
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	5		5		21
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 11,303		$ 11,303		$ 58,451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 180		$ 180		$ 842
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	316		316		383
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 1,151,274		$ 1,151,274		$ 1,624,891
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13,670		13,670		$ 38,783
Net gains (losses) on other financial instruments	575	1,262	677	2,896
Net Gains (Losses) on Investments and Other Financial Instruments	5,331	30,527	2,480	61,813
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	(1,180)	1,166	(3,689)	(1,982)
Equity securities
Gain (Loss) on Investments [Line Items]
Available-for-sale Securities, Gross Realized (Loss) Gain, Excluding Other than Temporary Impairments	385	0	385	(170)
Trading Securities [Member]
Gain (Loss) on Investments [Line Items]
Trading securities	(349)	421	(6,043)	(1,819)
Short-term Investments [Member]
Gain (Loss) on Investments [Line Items]
Short-term investments	$ (38)	$ 0	$ (32)	$ (39)
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	10		10		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 47,282		$ 47,282		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 340		$ 340		$ 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	10		10		7
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 47,282		$ 47,282		$ 30,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 340		$ 340		$ 821