REGULATORY MATTERS, COMMITMENTS AND CONTINGENCIES- Regulatory Capital Positions (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Holding Company [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital (to Risk-Weighted Assets)	$ 2,358,608	$ 2,286,337
Total Capital (to Risk-Weighted Assets) Ratio	20.32%	25.22%
Total Capital (to Risk-Weighted Assets) Required For Capital Adequacy	$ 928,727	$ 725,236
Total Capital (to Risk-Weighted Assets) Required For Capital Adequacy Ratio	8.00%	8.00%
Common Equity Tier One Capital	$ 1,998,067	$ 1,957,887
Common Equity Tier One Capital (to Risk-Weighted Assets) Ratio	17.21%	21.60%
Common Equity Tier One Capital Required for Capital Adequacy	$ 522,409	$ 407,946
Common Equity Tier One Capital (to Risk-Weighted Assets) Required for Capiral Adequacy Ratio	4.50%	4.50%
Tier One Capital (to Risk-Weighted Assets)	$ 2,034,171	$ 1,993,991
Tier One Capital (to Risk-Weighted Assets) Ratio	17.52%	22.00%
Tier One Capital (to Risk-Weighted Assets) Required For Capital Adequacy	$ 696,545	$ 543,927
Tier One Capital (to Risk-Weighted Assets) Required For Capital Adequacy Ratio	6.00%	6.00%
Leverage ratio, amount	$ 2,034,171	$ 1,993,991
Leverage Ratio, ratio	13.04%	16.15%
Leverage Ratio Required Fo Capital Adequacy Ratio	4.00%	4.00%
Leverage Ratio Required For Capital Adequacy	$ 623,885	$ 493,786
FirstBank [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital (to Risk-Weighted Assets)	$ 2,300,760	$ 2,242,262
Total Capital (to Risk-Weighted Assets) Ratio	19.83%	24.74%
Total Capital (to Risk-Weighted Assets) Required For Capital Adequacy	$ 928,372	$ 725,047
Total Capital (to Risk-Weighted Assets) Required For Capital Adequacy Ratio	8.00%	8.00%
Total Capital (to Risk-Weighted Assets) Required To Be Well Capitalized	$ 1,160,465	$ 906,309
Total Capital (to Risk-Weighted Assets) Required To Be Well Capitalized Ratio	10.00%	10.00%
Common Equity Tier One Capital	$ 1,846,628	$ 1,820,571
Common Equity Tier One Capital (to Risk-Weighted Assets) Ratio	15.91%	20.09%
Common Equity Tier One Capital Required for Capital Adequacy	$ 522,209	$ 407,839
Common Equity Tier One Capital (to Risk-Weighted Assets) Required for Capiral Adequacy Ratio	4.50%	4.50%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 754,302	$ 589,101
Common Equity Tier One Capital (to Risk-Weighted Assets) Required To Be Well Capitalized Ratio	6.50%	6.50%
Tier One Capital (to Risk-Weighted Assets)	$ 2,154,628	$ 2,128,571
Tier One Capital (to Risk-Weighted Assets) Ratio	18.57%	23.49%
Tier One Capital (to Risk-Weighted Assets) Required For Capital Adequacy	$ 696,279	$ 543,785
Tier One Capital (to Risk-Weighted Assets) Required For Capital Adequacy Ratio	6.00%	6.00%
Tier One Capital (to Risk-Weighted Assets) Required To Be Well Capitalized	$ 928,372	$ 725,047
Tier One Capital (to Risk-Weighted Assets) Required To Be Well Capitalized Ratio	8.00%	8.00%
Leverage ratio, amount	$ 2,154,628	$ 2,128,571
Leverage Ratio, ratio	13.83%	17.26%
Leverage Ratio Required Fo Capital Adequacy Ratio	4.00%	4.00%
Leverage Ratio Required To Be Well Capitalized	$ 779,223	$ 616,552
Leverage Ratio Required For Capital Adequacy	$ 623,378	$ 493,242
Leverage Ratio Required To Be Well Capitalized Ratio	5.00%	5.00%

Common Equity Tier 1 capital divided by risk weighted assets as defined by new Basel III rule.

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Common Equity Tier 1 capital divided by risk weighted assets for capital adequacy as defined by new Basel III rule.

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Common Equity Tier 1 capital divided by risk weighted assets to be well capitalized as defined by new Basel III rule.

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Amount of Common Equity Tier One Risk-based Capital, as defined by regulatory framework.

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Amount of Common Equity Tier 1 Risk-based Capital required to be categorized as adequately capitalized under regulatory framework for prompt corrective action.

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

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The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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

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