REGULATORY MATTERS: (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Corporation 2013
Capital [Abstract]
Capital	$ 386,622
Capital to Risk Weighted Assets (percent)	17.86%
Capital Required for Capital Adequacy	173,211
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.00%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	367,783
Tier One Risk Based Capital to Risk Weighted Assets (percent)	16.99%
Tier One Risk Based Capital Required for Capital Adequacy	86,605
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	4.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	367,783
Tier One Leverage Capital to Average Assets (percent)	12.33%
Tier One Leverage Capital Required for Capital Adequacy	119,356
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	4.00%
Corporation 2012
Capital [Abstract]
Capital		375,601
Capital to Risk Weighted Assets (percent)		17.13%
Capital Required for Capital Adequacy		175,372
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)		8.00%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital		355,533
Tier One Risk Based Capital to Risk Weighted Assets (percent)		16.22%
Tier One Risk Based Capital Required for Capital Adequacy		87,686
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)		4.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital		355,533
Tier One Leverage Capital to Average Assets (percent)		11.69%
Tier One Leverage Capital Required for Capital Adequacy		121,622
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)		4.00%
First Financial Bank 2013
Capital [Abstract]
Capital	358,631
Capital to Risk Weighted Assets (percent)	17.13%
Capital Required for Capital Adequacy	167,472
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	8.00%
Capital Required to be Well Capitalized	209,340
Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	10.00%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital	342,452
Tier One Risk Based Capital to Risk Weighted Assets (percent)	16.36%
Tier One Risk Based Capital Required for Capital Adequacy	83,736
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)	4.00%
Tier One Risk Based Capital Required to be Well Capitalized	125,604
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets (percent)	6.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital	342,452
Tier One Leverage Capital to Average Assets (percent)	11.83%
Tier One Leverage Capital Required for Capital Adequacy	115,770
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)	4.00%
Tier One Leverage Capital Required to be Well Capitalized	144,712
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (percent)	5.00%
First Financial Bank 2012
Capital [Abstract]
Capital		349,968
Capital to Risk Weighted Assets (percent)		16.49%
Capital Required for Capital Adequacy		169,745
Capital Required for Capital Adequacy to Risk Weighted Assets (percent)		8.00%
Capital Required to be Well Capitalized		212,181
Capital Required to be Well Capitalized to Risk Weighted Assets (percent)		10.00%
Tier One Risk Based Capital [Abstract]
Tier One Risk Based Capital		332,644
Tier One Risk Based Capital to Risk Weighted Assets (percent)		15.68%
Tier One Risk Based Capital Required for Capital Adequacy		84,872
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets (percent)		4.00%
Tier One Risk Based Capital Required to be Well Capitalized		127,309
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets (percent)		6.00%
Tier One Leverage Capital [Abstract]
Tier One Leverage Capital		332,644
Tier One Leverage Capital to Average Assets (percent)		11.40%
Tier One Leverage Capital Required for Capital Adequacy		116,711
Tier One Leverage Capital Required for Capital Adequacy to Average Assets (percent)		4.00%
Tier One Leverage Capital Required to be Well Capitalized		$ 145,889
Tier One Leverage Capital Required to be Well Capitalized to Average Assets (percent)		5.00%