Note 20 - Selected Quarterly Financial Data (Details) - USD ($) $ in Thousands	3 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
Net Operating Revenues	$ 233,927	$ 225,386	$ 224,902	$ 222,407	$ 226,374	$ 218,223	$ 216,555	$ 210,531
Income Before Non-Operating Income	20,223	13,761	15,706	17,436	20,204	14,736	16,083	16,988
Non-Operating Income	5,246	4,550	4,130	4,222	4,392	3,937	4,281	4,572
Net Income	14,976	12,567	12,358	13,242	14,800	12,829	12,511	13,229
Preferred Dividends	332	2,152	2,167	2,168	2,168	2,167	2,167	2,168
Net Income Available to Common Stockholders	$ 14,644	$ 10,415	$ 10,191	$ 11,074	$ 12,632	$ 10,662	$ 10,344	$ 11,061
Basic Earnings Per Share (in dollars per share)	$ 1.03	$ 0.75	$ 0.74	$ 0.80	$ 0.92	$ 0.77	$ 0.75	$ 0.80
Diluted Earnings Per Share (in dollars per share)	$ 0.99	$ 0.72	$ 0.71	$ 0.77	$ 0.88	$ 0.75	$ 0.72	$ 0.78