Note 8 - Business Segment Information - Selected Financial Information on the Company's Business Segments (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Total revenue	$ 58,639,296			$ 40,542,168			$ 156,437,521	$ 118,406,807
Net interest income	38,313,483			28,556,348			102,800,897	84,271,928
Provision for loan/lease losses	6,205,828			2,086,436			11,046,402	6,214,538
Net income	8,808,835	$ 10,445,385	$ 10,549,961	7,853,935	$ 8,766,017	$ 9,184,965	29,804,181	25,804,917
Goodwill	73,618,426			13,110,913			73,618,426	13,110,913	$ 28,334,092
Core deposit intangible	16,136,914			6,688,613			16,136,914	6,688,613	9,078,953
Total assets	4,792,732,495			3,550,463,094			4,792,732,495	3,550,463,094	$ 3,982,664,773
Net income (loss)							29,804,181	25,804,917
Intersegment Eliminations [Member]
Total revenue	(12,707,109)			(7,052,986)			(38,449,680)	(27,283,484)
Net interest income	4,991						4,991
Net income	(12,467,390)			(9,994,703)			(37,832,216)	(29,996,740)
Total assets	(537,349,129)			(385,609,794)			(537,349,129)	(385,609,794)
Commercial Banking Segment [Member] | Quad City Bank and Trust Company [Member] | Operating Segments [Member]
Total revenue	17,321,929			11,771,842			49,812,373	39,517,823
Net interest income	12,218,192			11,664,970			36,628,528	34,381,270
Provision for loan/lease losses	409,086			1,140,436			2,783,988	2,624,538
Net income	4,827,397			3,929,158			13,796,167	11,657,941
Goodwill	3,222,688			3,222,688			3,222,688	3,222,688
Total assets	1,579,327,112			1,456,251,244			1,579,327,112	1,456,251,244
Commercial Banking Segment [Member] | Cedar Rapids Bank and Trust [Member] | Operating Segments [Member]
Total revenue	16,799,795			10,892,025			49,301,104	31,428,339
Net interest income	10,832,532			7,903,483			32,149,435	22,107,955
Provision for loan/lease losses	452,742			200,000			1,682,312	750,000
Net income	4,868,765			3,130,319			14,190,335	8,893,461
Goodwill	14,979,984						14,979,984
Core deposit intangible	3,313,000			1,122,263			3,313,000	1,122,263
Total assets	1,354,294,043			1,007,062,151			1,354,294,043	1,007,062,151
Commercial Banking Segment [Member] | Community State Bank [Member] | Operating Segments [Member]
Total revenue	8,888,955			7,678,006			25,458,573	23,981,019
Net interest income	7,101,066			6,379,111			20,579,523	20,326,439
Provision for loan/lease losses	20,000			574,000			816,602	2,209,000
Net income	2,533,392			1,669,209			6,560,327	5,484,383
Goodwill	9,888,225			9,888,225			9,888,225	9,888,225
Core deposit intangible	4,852,300			5,566,350			4,852,300	5,566,350
Total assets	734,535,978			631,963,143			734,535,978	631,963,143
Commercial Banking Segment [Member] | Rockford Bank and Trust [Member] | Operating Segments [Member]
Total revenue	5,244,856			4,534,768			15,362,717	12,723,998
Net interest income	3,414,760			3,245,346			10,281,763	9,308,932
Provision for loan/lease losses	4,849,000			172,000			5,288,500	631,000
Net income	(2,519,016)			726,926			(964,098)	2,406,337
Total assets	484,059,163			445,098,530			484,059,163	445,098,530
Commercial Banking Segment [Member] | SPRINGFIELD BANCSHARES, INC | Operating Segments [Member]
Total revenue	7,360,191						7,360,191
Net interest income	5,700,566						5,700,566
Provision for loan/lease losses	475,000						475,000
Net income	2,197,448						2,197,448
Goodwill	45,527,529						45,527,529
Core deposit intangible	7,971,614						7,971,614
Total assets	623,519,770						623,519,770
Wealth Management Segment [Member] | Operating Segments [Member]
Total revenue	3,255,241			2,689,853			9,560,319	7,952,495
Net income	768,095			539,091			2,335,871	1,554,618
Other Segments [Member] | Operating Segments [Member]
Total revenue	12,475,438			10,028,660			38,031,924	30,086,617
Net interest income	(958,624)			(636,562)			(2,543,909)	(1,852,668)
Net income	8,600,144			7,853,935			29,520,347	25,804,917
Total assets	$ 554,345,558			$ 395,697,820			$ 554,345,558	$ 395,697,820