Note 7 - Business Segment Information - Selected Financial Information on the Company's Business Segments (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Total revenue	$ 49,710,480		$ 39,235,786		$ 97,798,225	$ 77,864,639
Net interest income	32,084,496		28,046,697		64,487,414	55,715,580
Provision for loan/lease losses	2,300,735		2,022,993		4,840,574	4,128,102
Net income	10,445,385	$ 10,549,961	8,766,017	$ 9,184,965	20,995,346	17,950,982
Goodwill	28,090,897		13,110,913		28,090,897	13,110,913	$ 28,334,092
Core deposit intangible	8,469,851		6,919,480		8,469,851	6,919,480	9,078,953
Total assets	4,106,882,705		3,457,186,695		4,106,882,705	3,457,186,695	$ 3,982,664,773
Operating Segments [Member] | Commercial Banking Segment [Member] | Quad City Bank and Trust Company [Member]
Total revenue	16,682,874		14,210,040		32,490,444	27,745,981
Net interest income	12,290,034		11,414,818		24,410,336	22,716,300
Provision for loan/lease losses	1,254,493		552,993		2,374,902	1,484,102
Net income	4,510,902		4,073,777		8,968,770	7,728,783
Goodwill	3,222,688		3,222,688		3,222,688	3,222,688
Total assets	1,563,643,434		1,400,307,827		1,563,643,434	1,400,307,827
Operating Segments [Member] | Commercial Banking Segment [Member] | Cedar Rapids Bank and Trust [Member]
Total revenue	16,503,977		10,149,769		32,501,309	20,536,314
Net interest income	10,481,055		7,230,425		21,316,903	14,204,472
Provision for loan/lease losses	627,742		300,000		1,229,570	550,000
Net income	4,705,042		2,870,582		9,321,570	5,763,142
Goodwill	14,979,984				14,979,984
Core deposit intangible	3,439,864		1,172,141		3,439,864	1,172,141
Total assets	1,345,431,093		993,768,912		1,345,431,093	993,768,912
Operating Segments [Member] | Commercial Banking Segment [Member] | Community State Bank [Member]
Total revenue	8,406,295		8,171,307		16,569,618	16,303,013
Net interest income	6,734,510		6,920,820		13,478,457	13,947,328
Provision for loan/lease losses	221,000		861,000		796,602	1,635,000
Net income	2,158,347		1,920,040		4,026,935	3,815,174
Goodwill	9,888,225		9,888,225		9,888,225	9,888,225
Core deposit intangible	5,029,987		5,747,339		5,029,987	5,747,339
Total assets	712,138,515		642,761,140		712,138,515	642,761,140
Operating Segments [Member] | Commercial Banking Segment [Member] | Rockford Bank and Trust [Member]
Total revenue	5,119,916		4,241,431		10,117,861	8,189,230
Net interest income	3,401,849		3,095,512		6,867,003	6,063,586
Provision for loan/lease losses	197,500		309,000		439,500	459,000
Net income	813,623		834,842		1,554,918	1,679,411
Total assets	484,123,277		426,159,677		484,123,277	426,159,677
Operating Segments [Member] | Wealth Management Segment [Member]
Total revenue	3,115,653		2,560,836		6,305,078	5,262,642
Net income	796,911		454,465		1,567,776	1,015,527
Operating Segments [Member] | Other Segments [Member]
Total revenue	13,024,443		10,181,814		25,556,486	20,057,957
Net interest income	(822,952)		(614,878)		(1,585,285)	(1,216,106)
Net income	10,405,693		8,766,014		20,920,203	17,950,982
Total assets	463,206,792		382,407,292		463,206,792	382,407,292
Intersegment Eliminations [Member]
Total revenue	(13,142,678)		(10,279,411)		(25,742,571)	(20,230,498)
Net income	(12,945,133)		(10,153,703)		(25,364,826)	(20,002,037)
Total assets	$ (461,660,406)		$ (388,218,153)		$ (461,660,406)	$ (388,218,153)