COVERED LOANS - Carrying Value of Purchased Impaired and Nonimpaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	$ 825,515		$ 1,053,244
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	121,745		195,892
Real estate-construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	12,898		17,120
Real estate-commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	512,320		637,044
Real estate-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	105,113		121,117
Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	9,892		13,176
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	60,502		64,978
All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	3,045		3,917
Loans Accounted for Under FASB ASC Topic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	748,825		964,388
Loans Accounted for Under FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	114,574		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	12,898		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	504,453		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	105,113		121,117
Loans Accounted for Under FASB ASC Topic 310-30 | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	9,108		12,123
Loans Accounted for Under FASB ASC Topic 310-30 | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	2,679		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	76,690	[1]	88,856	[1]
Loans Excluded from FASB ASC Topic 310-30 | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Purchased Loans	7,171	[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	7,867	[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	784	[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	57,823	[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	$ 3,045	[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.