LOANS (covered) - Carrying Value of Purchased Impaired and Nonimpaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 903,862		$ 1,053,244
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	142,009		195,892
Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	15,333		17,120
Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	556,673		637,044
Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	111,720		121,117
Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	11,641		13,176
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	63,162		64,978
All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	3,324		3,917
Loans Accounted for Under FASB ASC Topic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	822,965		964,388
Loans Accounted for Under FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	133,165		182,625
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	15,333		17,120
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	548,626		627,257
Loans Accounted for Under FASB ASC Topic 310-30 | Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	111,720		121,117
Loans Accounted for Under FASB ASC Topic 310-30 | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	10,791		12,123
Loans Accounted for Under FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	3,330		4,146
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	80,897	[1]	88,856	[1]
Loans Excluded from FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	8,844	[1]	13,267	[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	8,047	[1]	9,787	[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	850	[1]	1,053	[1]
Loans Excluded from FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	59,832	[1]	60,832	[1]
Loans Excluded from FASB ASC Topic 310-30 | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 3,324	[1]	$ 3,917	[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.