Note 6 - Fair Value Measurements - Summary of Activity for Metro Bonds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change due to accretion of principal	$ 1,700	$ 1,400	$ 1,400
Metropolitan District Bond Securities [Member]
Balance at beginning of period	25,911	18,203
Increase in fair value (recorded in other comprehensive income)	3,683	6,961
Change due to accretion of principal	1,747	1,427
Cash receipts	(1,179)	(680)
Balance at end of period	$ 30,162	$ 25,911	$ 18,203