Note 2 - Summary of Significant Accounting Policies - Earnings Per Common Share (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
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
Weighted average common shares outstanding (in shares)	28,850	28,861	29,022	29,097	28,862	28,927	29,246	29,397	28,957	29,106	29,788
Weighted average common stock equivalents (in shares)									13	20	29
Total weighted average common shares outstanding and common stock equivalents (in shares)	28,860	28,875	29,034	29,111	28,879	28,946	29,268	29,419	28,970	29,126	29,817
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
Dividend Payout ratio									30.40%	40.30%	40.30%