Note 21 - Selected Quarterly Financial Data (Detail) - Selected Quarterly Financial Data (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Operating Revenues	$ 194,043	$ 189,368	$ 187,765	$ 190,086	$ 192,742	$ 197,064	$ 190,783	$ 192,948	$ 761,262	$ 773,537	$ 720,653
Income Before Non-Operating Income	18,135	16,671	16,487	14,742	16,481	17,944	17,040	25,881	66,035	77,346	57,627
Non-Operating Income	6,699	6,771	5,907	5,868	5,677	5,140	5,155	4,561
Net Income	14,434	17,233	13,614	12,676	14,526	17,211	13,611	18,724	57,957	64,072	52,695
Preferred Dividends	2,168	2,167	2,168	2,168	2,168	2,167	2,168	2,168	8,671	8,671	8,673
Net Income Available to Common Stockholders	$ 12,266	$ 15,066	$ 11,446	$ 10,508	$ 12,358	$ 15,044	$ 11,443	$ 16,556	$ 49,286	$ 55,401	$ 44,022
Basic Earnings Per Share (in Dollars per share)	$ 0.88	$ 1.09	$ 0.83	$ 0.76	$ 0.89	$ 1.09	$ 0.83	$ 1.21	$ 3.56	$ 4.02	$ 3.22
Diluted Earnings Per Share (in Dollars per share)	$ 0.87	$ 1.04	$ 0.82	$ 0.76	$ 0.88	$ 1.05	$ 0.83	$ 1.15	$ 3.49	$ 3.90	$ 3.22