LOANS (covered) - Carrying Value of Purchased Impaired and Nonimpaired Loans (Detail) (USD $) In Thousands	Sep. 30, 2011		Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 1,151,066		$ 1,481,493
Loans Accounted for Under FASB ASC Topic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	1,055,568		1,350,138
Loans Accounted for Under FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	209,163		295,600
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	25,893		42,743
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	674,973		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	127,753		147,052
Loans Accounted for Under FASB ASC Topic 310-30 | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	13,022		19,560
Loans Accounted for Under FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	4,764		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	95,498	[1]	131,355	[1]
Loans Excluded from FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	14,719	[1]	38,439	[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 | Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	12,419	[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	1,156	[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	63,133	[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	4,071	[1]	7,168	[1]
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	223,882		334,039
Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	25,893		42,743
Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	687,392		855,725
Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	127,753		147,052
Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	14,178		21,071
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	67,897		73,695
All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 4,071		$ 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.