Note 21 - Quarterly Financial Data (Unaudited) - Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income	$ 56,019	$ 55,524	$ 55,091	$ 54,363	$ 52,468	$ 51,913	$ 50,222	$ 49,543	$ 220,997	$ 204,146	$ 197,128
Interest expense	13,668	13,811	13,202	13,230	13,052	12,603	12,082	11,989	53,911	49,726	49,554
Net interest income	42,351	41,713	41,889	41,133	39,416	39,310	38,140	37,554	167,086	154,420	147,574
Provision (benefit) for loan losses					664	(370)	(516)	(734)	0	(956)	(6,021)
Other operating income	15,426	1,853	37,717	2,540	2,145	1,697	9,947	1,930	57,536	15,719	10,243
Other operating expense	35,375	26,277	28,454	28,497	23,824	23,708	24,248	25,939	118,603	97,719	91,026
Income before income tax expense	22,402	17,289	51,152	15,176	17,073	17,669	24,355	14,279	106,019	73,376	72,812
Income tax benefit	8,116	6,655	20,717	5,615	5,439	6,661	9,521	5,546	41,103	27,167	28,573
Net income, as reported	$ 14,286	$ 10,634	$ 30,435	$ 9,561	$ 11,634	$ 11,008	$ 14,834	$ 8,733	$ 64,916	$ 46,209	$ 44,239
Basic earnings per common share (in dollars per share)	$ 0.50	$ 0.37	$ 1.05	$ 0.33	$ 0.40	$ 0.38	$ 0.51	$ 0.30	$ 2.24	$ 1.59	$ 1.49
Diluted earnings per common share (in dollars per share)	0.50	0.37	1.05	0.33	0.40	0.38	0.51	0.30	$ 2.24	$ 1.59	$ 1.48
Dividends per common share (in dollars per share)	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.16	$ 0.16	$ 0.16	$ 0.16
Basic earnings per share (in shares)	28,850	28,861	29,022	29,097	28,862	28,927	29,246	29,397	28,957	29,106	29,788
Diluted earnings per share (in shares)	28,860	28,875	29,034	29,111	28,879	28,946	29,268	29,419	28,970	29,126	29,817