Carrying Value of Purchased Impaired and Nonimpaired Loans (Detail) (USD $) In Thousands	Jun. 30, 2011		Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 1,242,730		$ 1,481,493
Loans Accounted for Under FASB ASC Topic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	1,143,484		1,350,138
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	40,811		42,743
Loans Accounted for Under FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	234,024		295,600
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	714,240		837,942
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	134,131		147,052
Loans Accounted for Under FASB ASC Topic 310-30 | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	13,989		19,560
Loans Accounted for Under FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	6,289		7,241
Loans Accounted for Under FASB ASC Topic 310-30 | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	0		0
Loans Excluded from FASB ASC Topic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	99,246	[1]	131,355	[1]
Loans Excluded from FASB ASC Topic 310-30 | Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	0	[1]	0	[1]
Loans Excluded from FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	17,729	[1]	38,439	[1]
Loans Excluded from FASB ASC Topic 310-30 | Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	12,645	[1]	17,783	[1]
Loans Excluded from FASB ASC Topic 310-30 | Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	0	[1]	0	[1]
Loans Excluded from FASB ASC Topic 310-30 | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	1,208	[1]	1,511	[1]
Loans Excluded from FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	62,375	[1]	66,454	[1]
Loans Excluded from FASB ASC Topic 310-30 | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	5,289	[1]	7,168	[1]
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	251,753		334,039
Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	40,811		42,743
Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	726,885		855,725
Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	134,131		147,052
Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	15,197		21,071
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	68,664		73,695
All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 5,289		$ 7,168

[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.