Note 19 - Quarterly Results of Operations (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
Revenues	$ 168,773	$ 171,346	$ 163,588	$ 161,287	$ 173,547	$ 171,550	$ 168,423	$ 159,409	$ 664,994	$ 672,929	$ 659,214
Operating income	15,237	14,354	14,161	17,311	16,392	13,042	12,932	8,640	61,063	51,006	51,995
Net income	$ 8,790	$ 8,410	$ 8,357	$ 10,188	$ 8,969	$ 7,652	$ 7,926	$ 5,287	$ 35,745	$ 29,834	$ 30,147
Basic earnings per common share (in dollars per share)	$ 0.26	$ 0.25	$ 0.25	$ 0.30	$ 0.27	$ 0.23	$ 0.24	$ 0.16	$ 1.07	$ 0.89	$ 0.91
Diluted earnings per common share (in dollars per share)	$ 0.26	$ 0.25	$ 0.25	$ 0.30	$ 0.27	$ 0.23	$ 0.24	$ 0.16	$ 1.06	$ 0.89	$ 0.90