Stockholders' Equity - Required Capital Amounts and Company's Respective Ratios (Detail) $ in Thousands	Sep. 30, 2016 USD ($)
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 708,421
Total Capital To Risk Weighted Assets Actual Ratio	15.06%
Capital Required For Capital Adequacy Amount	$ 376,350
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 405,752
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	8.625%
Common Equity Tier 1 Risk Based Capital Amount	$ 629,360
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	13.38%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 211,697
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	$ 241,099
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	5.125%
Tier 1 Risk Based Capital Amount	$ 660,360
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	14.04%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 282,262
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	$ 311,665
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	6.625%
Tier 1 Capital Amount	$ 660,360
Tier 1 Capital To Average Assets Ratio	9.89%
Tier 1 Capital Required For Capital Adequacy Amount	$ 267,195
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	$ 643,237
Total Capital To Risk Weighted Assets Actual Ratio	13.69%
Capital Required For Capital Adequacy Amount	$ 375,916
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%
Capital With Capital Conservation Buffer Amount	$ 405,284
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	8.625%
Capital Required To Be Well Capitalized Amount	$ 469,895
Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	10.00%
Common Equity Tier 1 Risk Based Capital Amount	$ 575,176
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	12.24%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 211,453
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	$ 240,821
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	5.125%
Common Equity Tier 1 Risk Based Capital Required To Be well Capitalized Amount	$ 305,432
Common Equity Tier 1 Risk Based Capital Required To Be well Capitalized Amount	6.50%
Tier 1 Risk Based Capital Amount	$ 595,176
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	12.67%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 281,937
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	$ 311,305
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	6.625%
Tier 1 Risk Based Capital Required To Be well Capitalized Amount	$ 375,916
Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	8.00%
Tier 1 Capital Amount	$ 595,176
Tier 1 Capital To Average Assets Ratio	8.92%
Tier 1 Capital Required For Capital Adequacy Amount	$ 266,755
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%
Tier 1 Capital Required To Be Well Capitalized Amount	$ 333,444
Tier 1 Capital Required To Be Well Capitalized To Average assets Ratio	5.00%