Stockholders' Equity - Required Capital Amounts and Company's Respective Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 886,190	$ 797,015
Total Capital To Risk Weighted Assets Actual Ratio	16.29%	15.62%
Capital Required For Capital Adequacy Amount	$ 435,208	$ 408,234
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%	8.00%
Capital With Capital Conservation Buffer Amount	$ 537,210	$ 472,020
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	9.875%	9.25%
Common Equity Tier 1 Risk Based Capital Amount	$ 808,801	$ 714,349
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	14.87%	14.00%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 244,804	$ 229,632
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	4.50%	4.50%
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 346,806	$ 293,418
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	6.375%	5.75%
Tier 1 Risk Based Capital Amount	$ 834,801	$ 745,349
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	15.35%	14.61%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 326,406	$ 306,175
Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	6.00%	6.00%
Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 428,408	$ 369,962
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.875%	7.25%
Tier 1 Capital Amount	$ 834,801	$ 745,349
Tier 1 Capital To Average Assets Ratio	11.09%	10.44%
Tier 1 Capital Required For Capital Adequacy Amount	$ 301,116	$ 285,444
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%	4.00%
BancFirst [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital Amount	$ 765,487	$ 714,964
Total Capital To Risk Weighted Assets Actual Ratio	14.09%	14.03%
Capital Required For Capital Adequacy Amount	$ 434,573	$ 407,698
Capital Required For Capital Adequacy to Risk Weighted Assets Ratio	8.00%	8.00%
Capital With Capital Conservation Buffer Amount	$ 536,426	$ 471,401
Capital With Capital Conservation To Risk Based Weighted Assets Buffer Ratio	9.875%	9.25%
Capital Required To Be Well Capitalized Amount	$ 543,216	$ 509,622
Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	10.00%	10.00%
Common Equity Tier 1 Risk Based Capital Amount	$ 694,098	$ 643,298
Common Equity Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	12.78%	12.62%
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 244,447	$ 229,330
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	4.50%	4.50%
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 346,300	$ 293,033
Common Equity Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	6.375%	5.75%
Common Equity Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 353,090	$ 331,255
Common Equity Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	6.50%	6.50%
Tier 1 Risk Based Capital Amount	$ 714,098	$ 663,298
Tier 1 Risk Based Capital To Risk Weighted Assets Ratio	13.15%	13.02%
Tier 1 Risk Based Capital Required For Capital Adequacy Amount	$ 325,930	$ 306,773
Tier 1 Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets Ratio	6.00%	6.00%
Tier 1 Risk Based Capital With Capital Conservation Buffer Amount	$ 427,783	$ 369,476
Tier 1 Risk Based Capital With Capital Conservation Buffer To Risk Weighted Assets Ratio	7.875%	7.25%
Tier 1 Risk Based Capital Required To Be Well Capitalized Amount	$ 434,573	$ 407,698
Tier 1 Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets Ratio	8.00%	8.00%
Tier 1 Capital Amount	$ 714,098	$ 663,298
Tier 1 Capital To Average Assets Ratio	9.49%	9.31%
Tier 1 Capital Required For Capital Adequacy Amount	$ 300,855	$ 285,101
Tier 1 Capital Required For Capital Adequacy To Average Assets Ratio	4.00%	4.00%
Tier 1 Capital Required To Be Well Capitalized Amount	$ 376,069	$ 356,677
Tier 1 Capital Required To Be Well Capitalized To Average Assets Ratio	5.00%	5.00%

Capital conservation buffer to risk weighted assets.

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The amount of total capital as defined in the regulations.

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Percentage of Common Equity Tier One Risk-based Capital to total risk-weighted assets, as defined by regulatory framework.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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