RETIREMENT PLANS: (Details Textual) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employer contributions	$ 5,078,000	$ 8,664,000
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	2,100,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(16,000)
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	79,869	73,560
Accumulated other comprehensive income (loss)	(7,472,000)	(10,494,000)
Pension and Other Postretirement Defined Benefit Plans, Liabilities	2,500,000	2,000,000
Percentage Of Plan Assets	49.00%	53.00%
First Financial Corporation Common Stock [Member]
Defined benefit plan assets equity securities	27,200,000	28,300,000
Equity Securities [Member]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	88.00%
Employee Stock Ownership Plan [Member]
Employer contributions	3,640,000	7,110,000	1,300,000
Employee Stock Ownership Plan (ESOP), Cash Contributions to ESOP	550,000
Defined Benefit Plan, Amortization of Net Transition Asset (Obligation)	60,000
Employee Stock Ownership Plan [Member] \| Equity Securities [Member]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	99.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	100.00%
Pension Plan [Member]
Pension Contributions	2,100,000
Pension Plan [Member] \| Equity Securities [Member]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	61.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	63.00%
Supplemental Employee Retirement Plans, Defined Benefit [Member]
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	68,000
Pension Expense	163,000	200,000
Accumulated other comprehensive income (loss)	402,000	91,000
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	59,000	120,000
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax	718,000	355,000
Post Retirement Medical Benefits [Member]
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	59,000
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	$ 60,000	$ 60,000	$ 60,000

Assets, equity stocks, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

No definition available.