Note 6 - Earnings Per Share - Summary of Earnings and Weighted Average Number of Common Shares Used in Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ 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
Weighted average common shares outstanding (in shares)									15,134,518	13,889,134	13,816,095
Net Income	$ 13,863	$ 11,110	$ 11,866	$ 13,699	$ 14,976	$ 12,567	$ 12,358	$ 13,242	$ 50,538	$ 53,143	$ 53,369
Dividends to preferred stockholders										6,819	8,670
Net income available to common stockholders	$ 13,863	$ 11,110	$ 11,866	$ 13,699	$ 14,644	$ 10,415	$ 10,191	$ 11,074	$ 50,538	$ 46,324	$ 44,699
Earnings per common share, basic (in dollars per share)	$ 0.92	$ 0.73	$ 0.78	$ 0.92	$ 1.03	$ 0.75	$ 0.74	$ 0.80	$ 3.34	$ 3.34	$ 3.24
Dilutive effect of contingent issuable stock (in shares)									48,303	456,323	328,669
Assumed average common shares outstanding (in shares)									15,206,997	14,491,433	14,222,133
Earnings per common share, diluted (in dollars per share)	$ 0.91	$ 0.73	$ 0.78	$ 0.91	$ 0.99	$ 0.72	$ 0.71	$ 0.77	$ 3.32	$ 3.20	$ 3.14
Employee Stock Option [Member]
Dilutive effect share-based awards (in shares)									24,176	144,793	73,678
Restricted Stock [Member]
Dilutive effect share-based awards (in shares)										1,183	3,691