REGULATORY MATTERS: (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Corporation [Member]
Capital [Abstract]
Capital	$ 411,713	$ 398,903
Capital to Risk Weighted Assets (percent)	18.26%	18.62%
Capital Required for Capital Adequacy	$ 194,435	$ 171,346
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.625%	8.00%
Common equity capital	$ 392,939	$ 378,957
Commen Equity Capital to Risk Weighted Assets	17.43%	17.69%
Common equity capital required for capital adequacy	$ 115,534	$ 96,382
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	5.125%	4.50%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	$ 392,939	$ 378,957
Tier One Risk Based Capital to Risk Weighted Assets (percent)	17.43%	17.69%
Tier One Risk Based Capital Required for Capital Adequacy	$ 149,348	$ 128,509
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	6.625%	6.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	$ 392,939	$ 378,957
Tier One Leverage Capital to Average Assets (percent)	13.39%	12.92%
Tier One Leverage Capital Required for Capital Adequacy	$ 117,376	$ 117,352
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	4.00%	4.00%
First Financial Bank [Member]
Capital [Abstract]
Capital	$ 384,522	$ 372,922
Capital to Risk Weighted Assets (percent)	17.64%	18.05%
Capital Required for Capital Adequacy	$ 188,003	$ 165,261
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.625%	8.00%
Capital Required to be Well Capitalized	$ 217,974	$ 206,576
Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	10.00%	10.00%
Common equity capital	$ 368,797	$ 355,853
Commen Equity Capital to Risk Weighted Assets	16.92%	17.23%
Common equity capital required for capital adequacy	$ 111,712	$ 92,959
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	5.125%	4.50%
Common equity capital required to be well capitalized	$ 141,683	$ 134,274
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	$ 368,797	$ 355,853
Tier One Risk Based Capital to Risk Weighted Assets (percent)	16.92%	17.23%
Tier One Risk Based Capital Required for Capital Adequacy	$ 144,408	$ 123,945
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	6.625%	6.00%
Tier One Risk Based Capital Required to be Well Capitalized	$ 174,379	$ 165,261
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	$ 368,797	$ 355,853
Tier One Leverage Capital to Average Assets (percent)	12.82%	12.50%
Tier One Leverage Capital Required for Capital Adequacy	$ 115,047	$ 113,888
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	$ 143,809	$ 142,360
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (percent)	5.00%	5.00%

Commen Equity Capital to Risk Weighted Assets

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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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Common equity capital required for capital adequacy

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Common equity capital required to be well capitalized

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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 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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