REGULATORY MATTERS: (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Corporation [Member]
Capital [Abstract]
Capital	$ 495,817	$ 451,036
Capital to Risk Weighted Assets (percent)	16.16%	19.36%
Capital Required for Capital Adequacy	$ 322,091	$ 230,091
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	10.50%	9.875%
Common equity capital	$ 475,874	$ 430,600
Commen Equity Capital to Risk Weighted Assets	15.51%	18.48%
Common equity capital required for capital adequacy	$ 214,728	$ 148,540
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	7.00%	6.375%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	$ 475,874	$ 430,600
Tier One Risk Based Capital to Risk Weighted Assets (percent)	15.51%	18.48%
Tier One Risk Based Capital Required for Capital Adequacy	$ 260,741	$ 183,490
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.50%	7.875%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	$ 475,874	$ 430,600
Tier One Leverage Capital to Average Assets (percent)	12.04%	14.59%
Tier One Leverage Capital Required for Capital Adequacy	$ 158,081	$ 118,072
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	4.00%	4.00%
First Financial Bank [Member]
Capital [Abstract]
Capital	$ 472,995	$ 421,553
Capital to Risk Weighted Assets (percent)	15.91%	18.71%
Capital Required for Capital Adequacy	$ 312,111	$ 222,453
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	10.50%	9.875%
Capital Required to be Well Capitalized	$ 297,249	$ 225,268
Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	10.00%	10.00%
Common equity capital	$ 457,649	$ 405,181
Commen Equity Capital to Risk Weighted Assets	15.40%	17.99%
Common equity capital required for capital adequacy	$ 208,074	$ 143,609
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	7.00%	6.375%
Common equity capital required to be well capitalized	$ 193,212	$ 146,424
Common Equity Capital required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	$ 457,649	$ 405,181
Tier One Risk Based Capital to Risk Weighted Assets (percent)	15.40%	17.99%
Tier One Risk Based Capital Required for Capital Adequacy	$ 252,661	$ 177,399
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.50%	7.875%
Tier One Risk Based Capital Required to be Well Capitalized	$ 237,799	$ 180,215
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	8.00%	8.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	$ 457,649	$ 405,181
Tier One Leverage Capital to Average Assets (percent)	11.93%	14.19%
Tier One Leverage Capital Required for Capital Adequacy	$ 153,453	$ 114,213
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized	$ 191,816	$ 142,767
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (percent)	5.00%	5.00%

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Common Equity Capital required to be Well Capitalized to Risk Weighted Assets

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Common equity capital

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

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