REGULATORY MATTERS, COMMITMENTS AND CONTINGENCIES - Regulatory capital positions (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Securitization of FHA/VA mortgage loan production into GNMA mortgage-backed securities	$ 338,300
To originate loans [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	41,271	$ 59,747
Unused personal lines of credit [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	667,552	687,585
Commercial lines of credit [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	421,437	361,226
Commercial Letters Of Credit [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	47,515	24,359
Standby letters of credit [Member] [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	2,556	3,577
Commitments To Sell Loans [Member]
Loss Contingencies [Line Items]
Financial instruments whose contract amounts represent credit risk	119,679	49,998
First Ban Corp [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital	1,921,329	1,828,559
Common Equity Tier 1 Capital To Risk Weight Assets	1,597,117	1,546,678
Tier 1 Capital	1,597,117	1,546,678
Tier 1 Leverage Capital	1,597,117	1,546,678
Total Capital Required For Capital Adequacy	720,329	731,164
Common Equity Tier 1 Capital To Risk Weight Assets Capital Adequacy	405,185	411,280
Tier 1 Risk Based Capital Required for Capital Adequacy	540,247	548,373
Tier 1 Leverage Capital Required for Capital Adequacy	$ 466,376	$ 506,322
Total Risk Based Capital Ratio	21.34%	20.01%
Common Equity Tier 1 Capital To Risk Weight Assets Ratio	17.74%	16.92%
Tier 1 Risk Based Capital Ratio	17.74%	16.92%
Tier 1 Leverage Ratio	13.70%	12.22%
Total Risk Based Capital Ratio Adequately Capitalized	8.00%	8.00%
Common Equity Tier 1 Capital To Risk Weight Assets Ratio Capital Adequacy	4.50%	4.50%
Tier 1 Risk Based Capital Ratio Adequately Capitalized	6.00%	6.00%
Tier 1 Leverage Ratio Adequately Capitalized	4.00%	4.00%
FirstBank [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital	$ 1,872,120	$ 1,802,711
Common Equity Tier 1 Capital To Risk Weight Assets	1,523,332	1,493,478
Tier 1 Capital	1,757,642	1,685,656
Tier 1 Leverage Capital	1,757,642	1,685,656
Total Capital Required For Capital Adequacy	720,091	730,824
Common Equity Tier 1 Capital To Risk Weight Assets Capital Adequacy	405,051	411,088
Tier 1 Risk Based Capital Required for Capital Adequacy	540,068	548,118
Tier 1 Leverage Capital Required for Capital Adequacy	465,740	505,648
Total Capital Required to be Well Capitalized	900,114	913,530
Common Equity Tier 1 Capital To Risk Weight Assets Well Capitalized	585,074	593,794
Tier 1 Risk Based Capital Required to be Well Capitalized	720,091	730,824
Tier 1 Leverage Capital Required to be Well Capitalized	$ 582,174	$ 632,060
Total Risk Based Capital Ratio	20.80%	19.73%
Common Equity Tier 1 Capital To Risk Weight Assets Ratio	16.92%	16.35%
Tier 1 Risk Based Capital Ratio	19.53%	18.45%
Tier 1 Leverage Ratio	15.10%	13.33%
Total Risk Based Capital Ratio Adequately Capitalized	8.00%	8.00%
Common Equity Tier 1 Capital To Risk Weight Assets Ratio Capital Adequacy	4.50%	4.50%
Tier 1 Risk Based Capital Ratio Adequately Capitalized	6.00%	6.00%
Tier 1 Leverage Ratio Adequately Capitalized	4.00%	4.00%
Total Risk Based Capital Ratio Well Capitalized	10.00%	10.00%
Common Equity Tier1 Capital To Risk Weight Assets Ratio Well Capitalized	6.50%	6.50%
Tier 1 Risk Based Capital to Risk Weighted Well Capitalized	8.00%	8.00%
Tier 1 Leverage Ratio Well Capitalized	5.00%	5.00%

Common Equity Tier 1 capital 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 as defined by new Basel III rule.

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Minimun common equity tier 1 capital to risk weight assets for well capitalized purposes plus capital conservation buffer as required by 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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Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

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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 minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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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 minimum Tier One Capital Ratio (Tier one 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 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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Represents the initial fair value recorded for liabilities incurred on transfer of financial assets in a securitization, asset-backed financing arrangement, or a similar transfer which transaction is recognized as a sale of the transferred financial assets.

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