Note 22 - Business Segment Information - Selected Financial Information on the Company's Business Segments (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenue									$ 224,420,336	$ 165,999,610	$ 137,502,624
Net interest income	$ 39,594,688	$ 38,313,483	$ 32,084,496	$ 32,402,918	$ 31,793,353	$ 28,556,348	$ 28,046,697	$ 27,668,883	142,395,585	116,065,281	94,516,777
Provision for loan/lease losses	1,612,047	6,205,828	2,300,735	2,539,839	2,255,381	2,086,436	2,022,993	2,105,109	12,658,449	8,469,919	7,478,166
Net income	13,315,518	$ 8,808,835	$ 10,445,385	$ 10,549,961	9,901,590	$ 7,853,935	$ 8,766,017	$ 9,184,965	43,119,699	35,706,507	27,686,787
Goodwill	77,831,902				28,334,092				77,831,902	28,334,092	13,110,913	$ 3,222,688
Core deposit intangible	17,450,182				9,078,953				17,450,182	9,078,953	7,381,213
Total assets	4,949,710,195				3,982,664,773				4,949,710,195	3,982,664,773	3,301,943,748
Net income (loss)									43,119,699	35,706,507	27,686,787
Intersegment Eliminations [Member]
Total revenue									(871,470)	(499,520)	4,100,975
Total assets	(26,387,315)				(26,924,088)				(26,387,315)	(26,924,088)	(33,126,711)
Guaranty Bank and Trust Company [Member]
Total revenue										1,806,078
Net interest income										1,551,356
Net income										346,835
Rockford Bank and Trust [Member]
Total revenue									20,848,171	18,035,971	16,043,894
Net interest income									13,638,969	12,707,651	11,887,201
Provision for loan/lease losses									4,618,833	728,000	900,000
Net income									667,809	2,660,364	3,235,711
Total assets	509,621,731				461,650,765				509,621,731	461,650,765	391,154,780
SPRINGFIELD BANCSHARES, INC
Total revenue									15,153,047
Net interest income									11,834,782
Provision for loan/lease losses									990,000
Net income									4,816,326
Goodwill	45,974,931								45,974,931
Core deposit intangible	7,734,501								7,734,501
Total assets	632,849,228								632,849,228
Commercial Banking Segment [Member] | Quad City Bank and Trust Company [Member] | Operating Segments [Member]
Total revenue									69,691,414	58,055,715	59,442,052
Net interest income									48,682,464	46,407,078	45,081,080
Provision for loan/lease losses									3,692,928	3,908,919	4,168,166
Net income									18,346,840	22,095,055	14,116,751
Goodwill	3,222,688				3,222,688				3,222,688	3,222,688	3,222,688
Total assets	1,623,368,583				1,541,777,558				1,623,368,583	1,541,777,558	1,395,785,241
Commercial Banking Segment [Member] | Cedar Rapids Bank and Trust [Member] | Operating Segments [Member]
Total revenue									69,864,300	45,367,035	37,242,901
Net interest income									43,038,038	31,042,302	29,205,047
Provision for loan/lease losses									1,833,226	1,050,000	950,000
Net income									20,044,067	10,712,174	12,317,545
Goodwill	14,979,984				15,223,179				14,979,984	15,223,179
Core deposit intangible	3,186,136				3,693,592				3,186,136	3,693,592	1,271,897
Total assets	1,379,222,278				1,307,376,687				1,379,222,278	1,307,376,687	913,055,738
Commercial Banking Segment [Member] | Community State Bank [Member] | Operating Segments [Member]
Total revenue									36,069,287	31,944,152	11,406,291
Net interest income									28,762,834	27,020,674	10,004,729
Provision for loan/lease losses									1,523,462	2,783,000	1,460,000
Net income									8,389,007	7,047,671	2,132,252
Goodwill	9,888,225				9,888,225				9,888,225	9,888,225	9,888,225
Core deposit intangible	4,674,613				5,385,361				4,674,613	5,385,361	6,109,316
Total assets	785,363,891				670,516,373				785,363,891	670,516,373	600,075,798
Wealth Management Segment [Member] | Operating Segments [Member]
Total revenue									13,432,963	11,057,519	9,156,948
Net income									2,951,991	2,241,494	1,665,453
Other Segments [Member] | Operating Segments [Member]
Total revenue									232,624	232,660	109,563
Net interest income									(3,561,502)	(2,663,780)	(1,661,280)
Net income									(12,096,341)	(9,397,086)	(5,780,925)
Goodwill	3,766,074								3,766,074
Core deposit intangible	1,854,932								1,854,932
Total assets	$ 45,671,799				$ 28,267,478				$ 45,671,799	$ 28,267,478	$ 34,998,902