Covered Loan Delinquency, excluding Loans Accounted for under FASB ASC Topic 310-30 (Detail) (USD $) In Thousands	Jun. 30, 2011		Dec. 31, 2010
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 1,242,730		$ 1,481,493
Covered Loans | Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	4,266		1,848
60 - 89 days past due	2,995		934
> 90 days past due	9,143		17,093
Total Past due	16,404		19,875
Current	82,842		111,480
Total	99,246		131,355
> 90 days past due and still accruing	0		9
Covered Loans | Loans Excluded from FASB ASC Topic 310-30 | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	1,346		880
60 - 89 days past due	1,875		419
> 90 days past due	5,189		13,764
Total Past due	8,410		15,063
Current	9,319		23,376
Total	17,729		38,439
> 90 days past due and still accruing	0		0
Covered Loans | Loans Excluded from FASB ASC Topic 310-30 | Real estate-commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	1,408		225
60 - 89 days past due	29		62
> 90 days past due	2,841		1,896
Total Past due	4,278		2,183
Current	8,367		15,600
Total	12,645		17,783
> 90 days past due and still accruing	0		0
Covered Loans | Loans Excluded from FASB ASC Topic 310-30 | Installment
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	1,208		1,511
Total	1,208		1,511
> 90 days past due and still accruing	0		0
Covered Loans | Loans Excluded from FASB ASC Topic 310-30 | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	1,353		656
60 - 89 days past due	1,086		443
> 90 days past due	1,103		1,424
Total Past due	3,542		2,523
Current	58,833		63,931
Total	62,375		66,454
> 90 days past due and still accruing	0		0
Covered Loans | Loans Excluded from FASB ASC Topic 310-30 | All other
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days past due	159		87
60 - 89 days past due	5		10
> 90 days past due	10		9
Total Past due	174		106
Current	5,115		7,062
Total	5,289		7,168
> 90 days past due and still accruing	0		9
Loans Excluded from FASB ASC Topic 310-30 | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	17,729	[1]	38,439	[1]
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	251,753		334,039
Loans Excluded from FASB ASC Topic 310-30 | Real estate-commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	12,645	[1]	17,783	[1]
Real estate-commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	726,885		855,725
Loans Excluded from FASB ASC Topic 310-30 | Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,208	[1]	1,511	[1]
Installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	15,197		21,071
Loans Excluded from FASB ASC Topic 310-30 | Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	62,375	[1]	66,454	[1]
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	68,664		73,695
Loans Excluded from FASB ASC Topic 310-30 | All other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	5,289	[1]	7,168	[1]
All other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	5,289		7,168
Loans Excluded from FASB ASC Topic 310-30
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 99,246	[1]	$ 131,355	[1]

[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.