Stockholders' Equity - Required Capital Amounts and Company's Respective Ratios (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 939,223
Total Capital To Risk Weighted Assets Actual Ratio	16.71%
Capital Required For Capital Adequacy Amount	$ 449,674
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 590,197
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	10.50%
Common Equity Tier 1 Risk Based Capital Amount	$ 858,115
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	15.27%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 252,942
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	4.50%
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 393,465
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.00%
Tier 1 Risk Based Capital Amount	$ 884,115
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	15.73%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 337,256
Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	6.00%
Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 477,779
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	8.50%
Tier 1 Capital Amount	$ 884,115
Tier 1 Capital To Average Assets Ratio	11.64%
Tier 1 Capital Required For Capital Adequacy Amount	$ 303,864
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%
BancFirst [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 813,627
Total Capital To Risk Weighted Assets Actual Ratio	14.50%
Capital Required For Capital Adequacy Amount	$ 448,824
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 589,082
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	10.50%
Capital Required To Be Well Capitalized Amount	$ 561,030
Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	10.00%
Common Equity Tier 1 Risk Based Capital Amount	$ 738,519
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	13.16%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 252,464
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	4.50%
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 392,721
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.00%
Common Equity Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 364,670
Common Equity Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	6.50%
Tier 1 Risk Based Capital Amount	$ 758,519
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	13.52%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 336,618
Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	6.00%
Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 476,876
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	8.50%
Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 448,824
Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	8.00%
Tier 1 Capital Amount	$ 758,519
Tier 1 Capital To Average Assets Ratio	10.01%
Tier 1 Capital Required For Capital Adequacy Amount	$ 303,252
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%
Tier 1 Capital Required To Be Well Capitalized Amount	$ 379,065
Tier 1 Capital Required To Be Well Capitalized To Average Assets Ratio	5.00%