Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Covered Loan and Non-Covered Loan Portfolios (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	$ 251,603	$ 193,761
(Reversal of) Provision for credit losses before benefit attributable to FDIC loss share agreements	(48,791)	3,541
Adjustment attributable to FDIC loss share agreements	45,414	(684)
Net (reversal of) provision for credit losses	(3,377)	2,857
Increase (Decrease) in FDIC loss share receivable	(45,414)	684
Transfer of balance to OREO	(11,877)	(5,363)
Loans charged-off	(2,103)	(15,537)
Recoveries	893	790
Balance, end of period	189,725	177,192
Non-Covered Loans Excluding Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	74,211	74,861
(Reversal of) Provision for credit losses before benefit attributable to FDIC loss share agreements	(4,002)	1,004
Adjustment attributable to FDIC loss share agreements
Net (reversal of) provision for credit losses	(4,002)	1,004
Increase (Decrease) in FDIC loss share receivable
Transfer of balance to OREO
Loans charged-off	(2,062)	(2,111)
Recoveries	893	772
Balance, end of period	69,040	74,526
Non-Covered Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	8,816
(Reversal of) Provision for credit losses before benefit attributable to FDIC loss share agreements	596	1,106
Adjustment attributable to FDIC loss share agreements
Net (reversal of) provision for credit losses	596	1,106
Increase (Decrease) in FDIC loss share receivable
Transfer of balance to OREO	(559)	(6)
Loans charged-off		(160)
Recoveries		1
Balance, end of period	8,853	941
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	168,576	118,900
(Reversal of) Provision for credit losses before benefit attributable to FDIC loss share agreements	(45,385)	1,431
Adjustment attributable to FDIC loss share agreements	45,414	(684)
Net (reversal of) provision for credit losses	29	747
Increase (Decrease) in FDIC loss share receivable	(45,414)	684
Transfer of balance to OREO	(11,318)	(5,357)
Loans charged-off	(41)	(13,266)
Recoveries		17
Balance, end of period	$ 111,832	$ 101,725