Note 16 - Selected Quarterly Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue	$ 17,717	$ 17,850	$ 17,892	$ 17,643	$ 18,178	$ 18,421	$ 18,488	$ 18,783	$ 71,102	$ 73,870	$ 78,972
Operating income	5,072	4,910	4,765	4,508	3,822	4,625	4,438	3,973	19,255	16,858	18,651
Net income	$ 1,844	$ 1,850	$ 1,655	$ 2,135	$ 940	$ 1,387	$ 1,308	$ 1,394	$ 7,484	$ 5,029	$ 109,144
Net income per common share-basic (in dollars per share)	$ 0.57	$ 0.57	$ 0.51	$ 0.66	$ 0.30	$ 0.45	$ 0.42	$ 0.45	$ 2.31	$ 1.62	$ 37.36
Net income per common share-diluted (in dollars per share)	$ 0.54	$ 0.56	$ 0.50	$ 0.65	$ 0.29	$ 0.44	$ 0.42	$ 0.45	$ 2.26	$ 1.59	$ 37.36