Note 12 - Segment and Related Information - Reconciliation of Financial Data from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Assets	$ 1,313,173		$ 1,321,537
Liabilities	1,161,648		1,170,440
Stockholders' equity	151,525	$ 141,729	151,097	$ 137,625
Interest and dividend income	12,329	12,296
Interest expense	1,796	1,862
Net interest income	10,533	10,434
Provision for Loan and Lease Losses, Total	2,500	25
Net interest income after provision for loan losses	8,033	10,409
Noninterest income (loss)	1,870	2,113
Noninterest expense	9,001	8,879
Undistributed net income of subsidiary
Income before income tax expense (benefit)	902	3,643
Income tax expense (benefit)	129	718
Net income	773	2,925
Reportable Legal Entities [Member] | Community Bank [ Member]
Assets	1,312,732		1,321,001
Liabilities	1,166,590		1,178,759
Stockholders' equity	146,142		142,242
Interest and dividend income	12,313	12,281
Interest expense	1,796	1,862
Net interest income	10,517	10,419
Provision for Loan and Lease Losses, Total	2,500	25
Net interest income after provision for loan losses	8,017	10,394
Noninterest income (loss)	1,044	958
Noninterest expense	8,021	7,901
Undistributed net income of subsidiary	213	118
Income before income tax expense (benefit)	1,253	3,569
Income tax expense (benefit)	130	661
Net income	1,123	2,908
Reportable Legal Entities [Member] | Exchange Underwriters, Inc [Member]
Assets	3,911		4,076
Liabilities	1,424		1,194
Stockholders' equity	2,487		2,882
Interest and dividend income	1	1
Interest expense
Net interest income	1	1
Provision for Loan and Lease Losses, Total
Net interest income after provision for loan losses	1	1
Noninterest income (loss)	1,281	1,147
Noninterest expense	975	975
Undistributed net income of subsidiary
Income before income tax expense (benefit)	307	173
Income tax expense (benefit)	94	55
Net income	213	118
Reportable Legal Entities [Member] | CB Financial Services, Inc [Member]
Assets	151,555		151,124
Liabilities	30		27
Stockholders' equity	151,525		151,097
Interest and dividend income	15	1,318
Interest expense
Net interest income	15	1,318
Provision for Loan and Lease Losses, Total
Net interest income after provision for loan losses	15	1,318
Noninterest income (loss)	(455)	8
Noninterest expense	5	3
Undistributed net income of subsidiary	1,123	1,604
Income before income tax expense (benefit)	678	2,927
Income tax expense (benefit)	(95)	2
Net income	773	2,925
Consolidation, Eliminations [Member]
Assets	(155,025)		(154,664)
Liabilities	(6,396)		(9,540)
Stockholders' equity	(148,629)		$ (145,124)
Interest and dividend income		(1,304)
Interest expense
Net interest income		(1,304)
Provision for Loan and Lease Losses, Total
Net interest income after provision for loan losses		(1,304)
Noninterest income (loss)
Noninterest expense
Undistributed net income of subsidiary	(1,336)	(1,722)
Income before income tax expense (benefit)	(1,336)	(3,026)
Income tax expense (benefit)
Net income	$ (1,336)	$ (3,026)