Note 5 - Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Beginning balance				$ 22,071
Ending balance		$ 26,001		26,001
Total ending AOCI		26,001		26,001
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Ending balance	[1]	26,001	$ 18,558	26,001	$ 18,558
Total ending AOCI	[1]	26,001	18,558	26,001	18,558
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Metropolitan District Bond Securities [Member]
Beginning balance	[1]	14,578	12,647	14,341	12,058
Other comprehensive income before reclassifications	[1]	247	567	484	1,156
Amounts reclassified from AOCI
Ending balance	[1]	14,825	13,214	14,825	13,214
Total ending AOCI	[1]	14,578	12,647	14,341	12,058
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Marketable Securities [Member]
Beginning balance	[1]	9,479	5,016	7,730	3,657
Other comprehensive income before reclassifications	[1]	2,389	880	4,423	1,404
Amounts reclassified from AOCI	[1],[2]	(692)	(552)	(977)	283
Ending balance	[1]	11,176	5,344	11,176	5,344
Total ending AOCI	[1]	$ 9,479	$ 5,016	$ 7,730	$ 3,657

[1] All amounts net-of-tax.

[2] See separate table below for details about these reclassifications.