Regulatory Matters (Regulatory Capital Levels And Related Ratios) (Details) $ in Thousands		Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (To Risk Weighted Assets), Ratio		12.50
Tier 1 Capital for Capital Adequacy (To Average Assets), Ratio		0.040
Common Equity Tier 1 Capital for Capital Adequacy (to Risk Weighted Assets), ratio		4.50%
Tier 1 Capital for Capital Adequacy (To Risk Weighted Assets), Ratio		0.060	0.040
Total Capital for Capital Adequacy (To Risk Weighted Assets), Ratio		0.080
Mid Penn Bancorp, Inc. [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital (To Average Assets)		$ 188,501	$ 168,146
Common Equity Tier 1 Capital (to Risk Weighted Assets)		188,501	168,146
Tier 1 Capital (To Risk Weighted Assets)		188,501	168,146
Total Capital (To Risk Weighted Assets)		$ 246,529	$ 204,811
Tier 1 Capital (to Average Assets), Ratio		0.068	0.078
Common Equity Tier 1 Capital (to Risk Weighted Assets), ratio		9.60%	9.80%
Tier 1 Capital (To Risk Weighted Assets), Ratio		0.096	0.098
Total Capital (To Risk Weighted Assets), Ratio		0.126	0.119
Tier 1 Capital for Capital Adequacy (To Average Assets)	[1]	$ 111,201	$ 86,773
Common Equity Tier 1 Capital for Capital Adequacy (to Risk Weighted Assets)	[1]	137,351	120,020
Tier 1 Capital for Capital Adequacy (To Risk Weighted Assets)	[1]	166,783	145,738
Total Capital for Capital Adequacy (To Risk Weighted Assets)	[1]	$ 206,026	$ 180,030
Tier 1 Capital for Capital Adequacy (To Average Assets), Ratio	[1]	0.0400	0.0400
Common Equity Tier 1 Capital for Capital Adequacy (to Risk Weighted Assets), ratio	[1]	7.00%	7.00%
Tier 1 Capital for Capital Adequacy (To Risk Weighted Assets), Ratio	[1]	0.0850	0.08500
Total Capital for Capital Adequacy (To Risk Weighted Assets), Ratio	[1]	0.1050	0.10500
Mid Penn Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital (To Average Assets)		$ 218,676	$ 185,101
Common Equity Tier 1 Capital (to Risk Weighted Assets)		218,676	185,101
Tier 1 Capital (To Risk Weighted Assets)		218,676	185,101
Total Capital (To Risk Weighted Assets)		$ 232,124	$ 204,196
Tier 1 Capital (to Average Assets), Ratio		0.079	0.085
Common Equity Tier 1 Capital (to Risk Weighted Assets), ratio		11.10%	10.80%
Tier 1 Capital (To Risk Weighted Assets), Ratio		0.111	0.108
Total Capital (To Risk Weighted Assets), Ratio		0.118	0.119
Tier 1 Capital for Capital Adequacy (To Average Assets)	[1]	$ 111,166	$ 86,760
Common Equity Tier 1 Capital for Capital Adequacy (to Risk Weighted Assets)	[1]	137,288	119,995
Tier 1 Capital for Capital Adequacy (To Risk Weighted Assets)	[1]	166,707	145,708
Total Capital for Capital Adequacy (To Risk Weighted Assets)	[1]	$ 205,933	$ 179,992
Tier 1 Capital for Capital Adequacy (To Average Assets), Ratio	[1]	0.0400	0.0400
Common Equity Tier 1 Capital for Capital Adequacy (to Risk Weighted Assets), ratio	[1]	7.00%	7.00%
Tier 1 Capital for Capital Adequacy (To Risk Weighted Assets), Ratio	[1]	0.0850	0.08500
Total Capital for Capital Adequacy (To Risk Weighted Assets), Ratio	[1]	0.1050	0.10500
Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Average Assets)		$ 138,958	$ 108,450
Common Equity Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets)		127,482	111,424
Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets)		156,901	137,137
Total Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets)		$ 196,126	$ 171,421
Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Average Assets), Ratio		0.050	0.050
Common Equity Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets), ratio		6.50%	6.50%
Tier 1 Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets), Ratio		0.080	0.080
Total Capital to be Well-Capitalized Under Prompt Corrective Action Provision (To Risk Weighted Assets), Ratio		0.100	0.100

[1] The minimum amounts and ratios as of December 31, 2020 and December 31, 2019 include the full phase in of the capital conservation buffer of 2.5 percent required by the Basel III framework.