Regulatory Capital - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Phantom section (for regulatory ratios):
Capital ($)	$ 674,310	$ 589,352
Capital to RWA (%)	0.1579	0.1882
Capital Required for Capital Adequacy ($)	$ 448,344	$ 328,865
Capital Required for Capital Adequacy to RWA (%)	0.1050	0.1050
Tier One Risk Based Capital ($)	$ 534,277	$ 458,325
Tier One Risk Based Capital to RWA (%)	0.1251	0.1463
Tier One Risk Based Capital Required for Capital Adequacy ($)	$ 362,945	$ 266,224
Tier One Risk Based Capital Required for Capital Adequacy to RWA (%)	0.0850	0.0850
Common Equity Tier One Risk Based Capital ($)	$ 515,082	$ 439,299
Common Equity Tier One Risk Based Capital To RWA (%)	0.1206	0.1403
Common Equity Tier One Risk Based Capital Required For Capital Adequacy ($)	$ 298,896	$ 219,243
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to RWA (%)	0.0700	0.0700
Tier One Leverage Capital to Average Assets	$ 534,277	$ 458,325
Tier One Leverage Capital to Average Assets (%)	0.0905	0.1022
Tier One Leverage Capital Required for Capital Adequacy ($)	$ 236,151	$ 179,302
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (%)	0.0400	0.0400
First Mid Bank
Phantom section (for regulatory ratios):
Capital ($)	$ 624,150	$ 446,308
Capital to RWA (%)	0.1467	0.1430
Capital Required for Capital Adequacy ($)	$ 446,711	$ 327,685
Capital Required for Capital Adequacy to RWA (%)	0.1050	0.1050
Capital Required to be Well Capitalized ($)	$ 425,439	$ 312,081
Capital Required to be Well Capitalized to RWA (%)	0.1000	0.1000
Tier One Risk Based Capital ($)	$ 578,517	$ 409,534
Tier One Risk Based Capital to RWA (%)	0.1360	0.1312
Tier One Risk Based Capital Required for Capital Adequacy ($)	$ 361,623	$ 265,269
Tier One Risk Based Capital Required for Capital Adequacy to RWA (%)	0.0850	0.0850
Tier One Risk Based Capital Required to be Well Capitalized ($)	$ 340,351	$ 249,665
Tier One Risk Based Capital Required to be Well Capitalized to RWA (%)	0.0800	0.0800
Common Equity Tier One Risk Based Capital ($)	$ 578,517	$ 409,534
Common Equity Tier One Risk Based Capital To RWA (%)	0.1360	0.1312
Common Equity Tier One Risk Based Capital Required For Capital Adequacy ($)	$ 297,807	$ 218,457
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to RWA (%)	0.0700	0.0700
Common Equity Tier One Risk Based Capital Required to Be Well Capitalized ($)	$ 276,535	$ 202,853
Common Equity Tier One Risk Based Capital Required To Be Well Capitalized to RiWA (%)	0.0650	0.0650
Tier One Leverage Capital to Average Assets	$ 578,517	$ 409,534
Tier One Leverage Capital to Average Assets (%)	0.0983	0.0918
Tier One Leverage Capital Required for Capital Adequacy ($)	$ 235,337	$ 178,497
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (%)	0.0400	0.0400
Tier One Leverage Capital Required to be Well Capitalized ($)	$ 294,171	$ 223,121
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (%)	0.0500	0.0500