COVERED LOANS - Covered Loan Delinquency, Excluding Loans Accounted for Under FASB ASC Topic 310-30 (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 825,515		$ 1,053,244
Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	76,690	[1]	88,856	[1]
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	121,745		195,892
Commercial | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	7,171	[1]	13,267	[1]
Real estate-commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	512,320		637,044
Real estate-commercial | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	7,867	[1]	9,787	[1]
Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	9,892		13,176
Installment | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	784	[1]	1,053	[1]
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	60,502		64,978
Home equity | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	57,823	[1]	60,832	[1]
All other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	3,045		3,917
All other | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	3,045	[1]	3,917	[1]
Covered Loans | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	481		1,611
60 - 89 days past due	1,458		311
> 90 days past due	4,769		10,164
Total Past due	6,708		12,086
Current	69,982		76,770
Total	76,690		88,856
> 90 days past due and still accruing	7		107
Covered Loans | Commercial | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	10		73
60 - 89 days past due	316		294
> 90 days past due	1,960		6,490
Total Past due	2,286		6,857
Current	4,885		6,410
Total	7,171		13,267
> 90 days past due and still accruing	0		0
Covered Loans | Real estate-commercial | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	0		184
60 - 89 days past due	0		0
> 90 days past due	941		1,870
Total Past due	941		2,054
Current	6,926		7,733
Total	7,867		9,787
> 90 days past due and still accruing	0		0
Covered Loans | Installment | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	0		0
60 - 89 days past due	0		0
> 90 days past due	0		0
Total Past due	0		0
Current	784		1,053
Total	784		1,053
> 90 days past due and still accruing	0		0
Covered Loans | Home equity | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	332		1,344
60 - 89 days past due	1,135		11
> 90 days past due	1,855		1,679
Total Past due	3,322		3,034
Current	54,501		57,798
Total	57,823		60,832
> 90 days past due and still accruing	0		0
Covered Loans | All other | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	139		10
60 - 89 days past due	7		6
> 90 days past due	13		125
Total Past due	159		141
Current	2,886		3,776
Total	3,045		3,917
> 90 days past due and still accruing	$ 7		$ 107

[1] Includes loans with revolving privileges which are scoped out of FASB ASC Topic 310-30 and certain loans which First Financial elected to treat under the cost recovery method of accounting.