Note 5 - Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Beginning balance		$ 22,071
Ending balance		24,057
Total ending AOCI		24,057
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Ending balance	[1]	24,057	$ 17,663
Total ending AOCI	[1]	24,057	17,663
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Metropolitan District Bond Securities [Member]
Beginning balance	[1]	14,341	12,058
Other comprehensive income before reclassifications	[1]	237	589
Amounts reclassified from AOCI
Ending balance	[1]	14,578	12,647
Total ending AOCI	[1]	14,341	12,058
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Marketable Securities [Member]
Beginning balance	[1]	7,730	3,657
Other comprehensive income before reclassifications	[1]	2,034	524
Amounts reclassified from AOCI	[1],[2]	(285)	835
Ending balance	[1]	9,479	5,016
Total ending AOCI	[1]	$ 7,730	$ 3,657

[1] All amounts net-of-tax.

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