REGULATORY MATTERS: (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Corporation [Member]
Capital [Abstract]
Capital	$ 533,599	$ 538,440
Capital to Risk Weighted Assets (percent)	0.1563	0.1740
Capital Required for Capital Adequacy	$ 358,575	$ 324,849
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	0.10500	0.10500
Common equity capital	$ 490,842	$ 499,664
Commen Equity Capital to Risk Weighted Assets	14.37%	16.15%
Common equity capital required for capital adequacy	$ 239,050	$ 216,566
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	7.00%	7.00%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	$ 490,842	$ 499,664
Tier One Risk Based Capital to Risk Weighted Assets (percent)	0.1437	0.1615
Tier One Risk Based Capital Required for Capital Adequacy	$ 290,275	$ 262,973
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	0.08500	0.08500
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	$ 490,842	$ 499,664
Tier One Leverage Capital to Average Assets (percent)	0.0983	0.1124
Tier One Leverage Capital Required for Capital Adequacy	$ 199,702	$ 177,781
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	0.0400	0.0400
First Financial Bank [Member]
Capital [Abstract]
Capital	$ 487,416	$ 507,869
Capital to Risk Weighted Assets (percent)	0.1478	0.1703
Capital Required for Capital Adequacy	$ 346,248	$ 313,075
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	0.10500	0.10500
Capital Required to be Well Capitalized	$ 329,760	$ 298,166
Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	0.1000	0.1000
Common equity capital	$ 446,189	$ 470,551
Commen Equity Capital to Risk Weighted Assets	13.53%	15.78%
Common equity capital required for capital adequacy	$ 230,832	$ 208,716
Common Equity Capital required for Capital Adequacy to Risk Weighted Assets	7.00%	7.00%
Common equity capital required to be well capitalized	$ 214,344	$ 193,808
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	$ 446,189	$ 470,551
Tier One Risk Based Capital to Risk Weighted Assets (percent)	0.1353	0.1578
Tier One Risk Based Capital Required for Capital Adequacy	$ 280,296	$ 253,441
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	0.08500	0.08500
Tier One Risk Based Capital Required to be Well Capitalized	$ 263,808	$ 238,533
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	0.0800	0.0800
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	$ 446,189	$ 470,551
Tier One Leverage Capital to Average Assets (percent)	0.0918	0.1090
Tier One Leverage Capital Required for Capital Adequacy	$ 194,405	$ 172,728
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	0.0400	0.0400
Tier One Leverage Capital Required to be Well Capitalized	$ 243,006	$ 215,910
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (percent)	0.0500	0.0500