Carrying Amount of Accretable Yield for Purchased Impaired and Nonimpaired Loans (Detail) (Covered Loans, USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	$ 461,290	[1]	$ 573,381	[1]	$ 509,945	[1]	$ 623,669	[1]
Additions	0		0		0		0
Reclassification from non-accretable difference	11,229		0		33,206		0
Accretion	(31,818)		(33,046)		(66,279)		(69,205)
Other net activity	(18,920)	[2]	(25,899)	[2]	(55,091)	[2]	(40,028)	[2]
Balance at end of period	$ 421,781		$ 514,436		$ 421,781		$ 514,436

[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.