Note 20 - Quarterly Financial Data (unaudited) (Detail) - Selected unaudited 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
Interest income	$ 51,722	$ 53,193	$ 54,384	$ 54,415	$ 54,644	$ 56,329	$ 56,499	$ 57,026	$ 213,714	$ 224,498	$ 229,628
Interest expense	14,498	15,610	16,097	17,070	17,920	19,228	19,704	19,871	63,275	76,723	91,767
Net interest income	37,224	37,583	38,287	37,345	36,724	37,101	36,795	37,155	150,439	147,775	137,861
Provision for loan losses	5,000	5,000	5,000	6,000	6,500	5,000	5,000	5,000	21,000	21,500	21,000
Other operating income	2,566	3,513	1,108	1,878	2,980	4,295	2,135	871	1,413	1,477	2,109
Other operating expense	19,808	20,743	20,239	21,536	19,369	19,490	18,865	20,015	82,326	77,739	70,385
Income before income tax expense	14,982	15,353	14,156	11,687	13,835	16,906	15,065	13,011	56,178	58,817	54,776
Income tax expense	5,782	5,988	5,519	4,558	5,664	6,756	5,991	5,058	21,847	23,469	15,941
Net income	$ 9,200	$ 9,365	$ 8,637	$ 7,129	$ 8,171	$ 10,150	$ 9,074	$ 7,953	$ 34,331	$ 35,348	$ 38,835
Basic earnings per common share (in Dollars per share)	$ 0.30	$ 0.31	$ 0.28	$ 0.23	$ 0.27	$ 0.33	$ 0.29	$ 0.26	$ 1.13	$ 1.15	$ 1.28
Diluted earnings per common share (in Dollars per share)	$ 0.30	$ 0.31	$ 0.28	$ 0.23	$ 0.27	$ 0.33	$ 0.29	$ 0.26	$ 1.13	$ 1.15	$ 1.28
Dividends per common share (in Dollars per share)	$ 0.13	$ 0.13	$ 0.13	$ 0.13	$ 0.13	$ 0.13	$ 0.13	$ 0.13
Basic earnings per share (in Shares)	30,310	30,432	30,472	30,396	30,371	30,679	30,823	30,620	30,402	30,623	30,336
Diluted earnings per share (in Shares)	30,340	30,462	30,492	30,420	30,387	30,693	30,864	30,686	30,433	30,654	30,367