Note 23 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) - USD ($)	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	$ 29,715,000,000	$ 29,706,000,000	$ 30,147,000,000	$ 28,889,000,000	$ 28,575,000,000	$ 28,501,000,000	$ 27,663,000,000	$ 27,589,000,000	$ 118,457,000	$ 112,328,000	$ 89,118,000
Net interest income	26,435,000,000	26,450,000,000	27,100,000,000	25,882,000,000	25,659,000,000	25,625,000,000	25,041,000,000	24,849,000,000	105,867,000	101,174,000	77,778,000
Net income attributable to common shares	$ 8,085,000,000	$ 7,845,000,000	$ 7,434,000,000	$ 8,549,000,000	$ 6,480,000,000	$ 7,336,000,000	$ 6,558,000,000	$ 6,646,000,000	$ 31,913,000	$ 27,020,000	$ 17,331,000
Earnings per share basic (in dollars per share)	$ 0.49	$ 0.48	$ 0.46	$ 0.52	$ 0.40	$ 0.45	$ 0.39	$ 0.39	$ 1.96	$ 1.63	$ 1.28
Earnings per share diluted (in dollars per share)	$ 0.49	$ 0.48	$ 0.46	$ 0.52	$ 0.40	$ 0.45	$ 0.39	$ 0.39	$ 1.96	$ 1.62	$ 1.28