Note 6 - Business Segment Information - Selected Financial Information on the Company's Business Segments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Total revenue	$ 38,628,853	$ 30,324,532
Net interest income	27,668,883	20,597,522
Provision for loan/lease losses	2,105,109	2,072,985
Net income (loss)	9,184,965	6,373,489
Goodwill	13,110,913	3,222,688	$ 13,110,913
Core deposit intangible	7,150,346	1,421,531	7,381,213
Total assets	3,381,012,618	2,640,673,254	$ 3,301,943,748
Operating Segments [Member] | Commercial Banking Segment [Member] | Quad City Bank and Trust Company [Member]
Total revenue	13,535,941	13,516,932
Net interest income	11,301,482	10,961,447
Provision for loan/lease losses	931,109	1,222,985
Net income (loss)	3,655,006	2,831,696
Goodwill	3,222,688	3,222,688
Core deposit intangible
Total assets	1,442,952,197	1,361,607,041
Operating Segments [Member] | Commercial Banking Segment [Member] | Cedar Rapids Bank and Trust [Member]
Total revenue	10,386,545	10,839,221
Net interest income	6,974,047	7,024,988
Provision for loan/lease losses	250,000	550,000
Net income (loss)	2,892,560	2,934,731
Goodwill
Core deposit intangible	1,222,019	1,421,531
Total assets	929,111,309	885,858,279
Operating Segments [Member] | Commercial Banking Segment [Member] | Community State Bank [Member]
Total revenue	8,131,706
Net interest income	7,026,508
Provision for loan/lease losses	774,000
Net income (loss)	1,895,134
Goodwill	9,888,225
Core deposit intangible	5,928,327
Total assets	608,431,003
Operating Segments [Member] | Commercial Banking Segment [Member] | Rockford Bank and Trust [Member]
Total revenue	3,947,799	3,794,247
Net interest income	2,968,074	2,911,974
Provision for loan/lease losses	150,000	300,000
Net income (loss)	844,569	617,785
Goodwill
Core deposit intangible
Total assets	398,454,864	367,031,670
Operating Segments [Member] | Wealth Management Segment [Member]
Total revenue	2,701,806	2,234,292
Net interest income
Provision for loan/lease losses
Net income (loss)	561,062	447,770
Goodwill
Core deposit intangible
Total assets
Operating Segments [Member] | Other Segments [Member]
Total revenue	9,876,143	6,859,775
Net interest income	(601,228)	(300,887)
Provision for loan/lease losses
Net income (loss)	9,184,968	6,373,488
Goodwill
Core deposit intangible
Total assets	377,316,912	288,814,613
Intersegment Eliminations [Member]
Total revenue	(9,951,087)	(6,919,935)
Net interest income
Provision for loan/lease losses
Net income (loss)	(9,848,334)	(6,831,981)
Goodwill
Core deposit intangible
Total assets	$ (375,253,667)	$ (262,638,349)