Regulatory Capital Requirements - Schedule of Regulatory Requirements (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Red River Bank
Total Risk-Based Capital
Actual Amount	$ 261,840	$ 238,021
Actual Ratio	0.1662	0.1623
Regulatory Requirements, Minimum, Amount	$ 126,031	$ 117,325
Regulatory Requirements, Minimum, Ratio	0.0800	0.0800
Regulatory Requirements, Minimum Plus CCB, Amount	$ 165,415	$ 153,989
Regulatory Requirements, Minimum Plus CCB, Ratio	0.1050	0.1050
Tier I Risk-Based Capital
Actual Amount	$ 245,648	$ 224,084
Actual Ratio	0.1559	0.1528
Regulatory Requirements, Minimum, Amount	$ 94,523	$ 87,994
Regulatory Requirements, Minimum, Ratio	0.0600	0.0600
Regulatory Requirements, Minimum Plus CCB, Amount	$ 133,908	$ 124,658
Regulatory Requirements, Minimum Plus CCB, Ratio	0.0850	0.0850
Common Equity Tier I Capital
Actual Amount	$ 245,648	$ 224,084
Actual Ratio	0.1559	0.1528
Regulatory Requirements, Minimum, Amount	$ 70,892	$ 65,995
Regulatory Requirements, Minimum, Ratio	0.0450	0.0450
Regulatory Requirements, Minimum Plus CCB, Amount	$ 110,277	$ 102,660
Regulatory Requirements, Minimum Plus CCB, Ratio	0.0700	0.0700
Tier I Leverage Capital
Actual Amount	$ 245,648	$ 224,084
Actual Ratio	0.1024	0.1147
Regulatory Requirements, Minimum, Amount	$ 95,933	$ 78,114
Regulatory Requirements, Minimum, Ratio	0.0400	0.0400
Regulatory Requirements, Minimum Plus CCB, Amount	$ 95,933	$ 78,114
Regulatory Requirements, Minimum Plus CCB, Ratio	0.0400	0.0400
Red River Bancshares, Inc.
Total Risk-Based Capital
Actual Amount	$ 286,324	$ 264,313
Actual Ratio	0.1817	0.1802
Tier I Risk-Based Capital
Actual Amount	$ 270,132	$ 250,376
Actual Ratio	0.1715	0.1707
Common Equity Tier I Capital
Actual Amount	$ 270,132	$ 250,376
Actual Ratio	0.1715	0.1707
Tier I Leverage Capital
Actual Amount	$ 270,132	$ 250,376
Actual Ratio	0.1126	0.1282