Stockholders' Equity - Required Capital Amounts and Company's Respective Ratios (Detail) $ in Thousands	Mar. 31, 2017 USD ($)
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 743,955
Total Capital To Risk Weighted Assets Actual Ratio	15.72%
Capital Required For Capital Adequacy Amount	$ 378,690
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 437,861
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	9.25%
Common Equity Tier 1 Risk Based Capital Amount	$ 665,034
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	14.05%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 213,013
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	$ 272,184
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	5.75%
Tier 1 Risk Based Capital Amount	$ 696,034
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	14.70%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 284,018
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	$ 343,188
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.25%
Tier 1 Capital Amount	$ 696,034
Tier 1 Capital To Average Assets Ratio	9.95%
Tier 1 Capital Required For Capital Adequacy Amount	$ 279,674
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	$ 668,329
Total Capital To Risk Weighted Assets Actual Ratio	14.14%
Capital Required For Capital Adequacy Amount	$ 378,252
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 437,354
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	9.25%
Capital Required To Be Well Capitalized Amount	$ 472,815
Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	10.00%
Common Equity Tier 1 Risk Based Capital Amount	$ 600,408
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	12.70%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 212,767
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	$ 271,869
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	5.75%
Common Equity Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 307,330
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	$ 620,408
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	13.12%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 283,689
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	$ 342,791
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.25%
Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 378,252
Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	8.00%
Tier 1 Capital Amount	$ 620,408
Tier 1 Capital To Average Assets Ratio	8.88%
Tier 1 Capital Required For Capital Adequacy Amount	$ 279,412
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%
Tier 1 Capital Required To Be Well Capitalized Amount	$ 349,266
Tier 1 Capital Required To Be Well Capitalized To Average Assets Ratio	5.00%