LOANS (covered) - Carrying Amount of Accretable Yield for Purchased Impaired and Nonimpaired Loans (Detail) (Covered Loans, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	$ 344,410	[1]	$ 509,945	[1]
Reclassification from non-accretable difference	14,384		21,977
Accretion	(25,919)		(34,461)
Other net activity	(19,206)	[2]	(36,171)	[2]
Balance at end of period	$ 313,669		$ 461,290

[1] Excludes loans with revolving privileges which are scoped out of FASB Topic 310-30 and certain loans which First Financial elected to treat under the cost recovery method.

[2] Includes the impact of loan repayments and charge-offs.