Note 18 - Earnings Per Share - Computation of Earnings Per Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income attributable to common shares	$ 13,317,000	$ 12,600,000	$ 11,715,000	$ 11,824,000	$ 11,574,000	$ 10,123,000	$ 9,446,000	$ 10,881,000	$ 49,456,000	$ 42,024,000	$ 31,274,000
Weighted average common shares outstanding (in shares)									16,405,159	16,600,612	16,478,968
Basic earnings per common share (in dollars per share)	$ 0.81	$ 0.77	$ 0.71	$ 0.72	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 3.01	$ 2.53	$ 1.90
Net income	$ 13,317,000	$ 12,600,000	$ 11,715,000	$ 11,824,000	$ 11,574,000	$ 10,123,000	$ 9,446,000	$ 10,881,000	$ 49,456,000	$ 42,024,000	$ 31,274,000
Weighted average common shares outstanding for basic earnings per common share (in shares)									16,405,159	16,600,612	16,478,968
Add: Dilutive effects of share-based awards (in shares)									3,976	5,804	10,102
Average shares and dilutive potential common shares (in shares)									16,409,135	16,606,416	16,489,070
Diluted earnings per common share (in dollars per share)	$ 0.81	$ 0.77	$ 0.71	$ 0.72	$ 0.70	$ 0.61	$ 0.57	$ 0.66	$ 3.01	$ 2.53	$ 1.90