Note 6 - Business Segment Information - Selected Financial Information on the Company's Business Segments (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Total revenue	$ 40,542,168			$ 37,240,136			$ 118,406,807	$ 98,240,353
Net interest income	28,556,348			23,630,777			84,271,928	65,237,112
Provision for loan/lease losses	2,086,436			1,607,986			6,214,538	4,878,821
Net income (loss)	7,853,935	$ 8,766,017	$ 9,184,965	6,107,501	$ 6,676,467	$ 6,373,489	25,804,917	19,157,457
Goodwill	13,110,913			13,631,626			13,110,913	13,631,626	$ 13,110,913
Core deposit intangible	6,688,613			7,613,593			6,688,613	7,613,593	7,381,213
Total assets	3,550,463,094			3,280,986,109			3,550,463,094	3,280,986,109	$ 3,301,943,748
Operating Segments [Member] | Commercial Banking Segment [Member] | Quad City Bank and Trust Company [Member]
Total revenue	11,771,842			18,026,215			39,517,823	45,706,061
Net interest income	11,664,970			11,225,414			34,381,270	33,394,620
Provision for loan/lease losses	1,140,436			1,137,986			2,624,538	3,108,821
Net income (loss)	3,929,158			3,596,469			11,657,941	10,326,508
Goodwill	3,222,688			3,222,688			3,222,688	3,222,688
Core deposit intangible
Total assets	1,456,251,244			1,407,733,009			1,456,251,244	1,407,733,009
Operating Segments [Member] | Commercial Banking Segment [Member] | Cedar Rapids Bank and Trust [Member]
Total revenue	10,892,025			10,065,032			31,428,339	31,342,345
Net interest income	7,903,483			7,594,557			22,107,955	21,755,270
Provision for loan/lease losses	200,000						750,000	700,000
Net income (loss)	3,130,319			3,286,724			8,893,461	9,366,441
Goodwill
Core deposit intangible	1,122,263			1,321,775			1,122,263	1,321,775
Total assets	1,007,062,151			887,592,695			1,007,062,151	887,592,695
Operating Segments [Member] | Commercial Banking Segment [Member] | Community State Bank [Member]
Total revenue	7,678,006			2,675,741			23,981,019	2,675,741
Net interest income	6,379,111			2,191,862			20,326,439	2,191,862
Provision for loan/lease losses	574,000			270,000			2,209,000	270,000
Net income (loss)	1,669,209			188,608			5,484,383	188,608
Goodwill	9,888,225			10,408,938			9,888,225	10,408,938
Core deposit intangible	5,566,350			6,291,818			5,566,350	6,291,818
Total assets	631,963,143			580,210,270			631,963,143	580,210,270
Operating Segments [Member] | Commercial Banking Segment [Member] | Rockford Bank and Trust [Member]
Total revenue	4,534,768			4,232,205			12,723,998	11,945,081
Net interest income	3,245,346			3,056,989			9,308,932	8,914,380
Provision for loan/lease losses	172,000			200,000			631,000	800,000
Net income (loss)	726,926			944,781			2,406,337	2,334,735
Goodwill
Core deposit intangible
Total assets	445,098,530			393,191,774			445,098,530	393,191,774
Operating Segments [Member] | Wealth Management Segment [Member]
Total revenue	2,689,853			2,284,577			7,952,495	6,723,690
Net interest income
Provision for loan/lease losses
Net income (loss)	539,091			398,859			1,554,618	1,232,831
Goodwill
Core deposit intangible
Total assets
Operating Segments [Member] | Other Segments [Member]
Total revenue	10,028,660			8,463,636			30,086,617	23,567,906
Net interest income	(636,562)			(438,045)			(1,852,668)	(1,019,020)
Provision for loan/lease losses
Net income (loss)	7,853,935			6,107,492			25,804,917	19,157,447
Goodwill
Core deposit intangible
Total assets	395,697,820			368,990,749			395,697,820	368,990,749
Intersegment Eliminations [Member]
Total revenue	(7,052,986)			(8,507,270)			(27,283,484)	(23,720,471)
Net interest income
Provision for loan/lease losses
Net income (loss)	(9,994,703)			(8,415,432)			(29,996,740)	(23,449,113)
Goodwill
Core deposit intangible
Total assets	$ (385,609,794)			$ (356,732,388)			$ (385,609,794)	$ (356,732,388)