Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Covered Loans, by Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	$ 251,603	$ 193,761
(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
Balance, end of period	8,405,250		8,246,977
Non-Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	83,027	74,861
(Reversal of) Provision for credit losses	(3,406)	2,110
Transfer of balance to OREO	(559)	(6)
Loans charged off	(2,062)	(2,271)
Recoveries	893	773
Balance, end of period	77,893	75,467
Allowance on loans individually evaluated for impairment	329	1,960
Allowance on loans collectively evaluated for impairment	77,564	73,507
Balance, end of period	7,590,802	6,217,644
Balance, end of period: Loans individually evaluated for impairment	31,599	41,852
Balance, end of period: Loans collectively evaluated for impairment	7,559,203	6,175,792
Balance, end of period: Loans acquired with deteriorated credit quality	58,501	45,125
Non-Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	38,264	35,604
(Reversal of) Provision for credit losses	(1,804)	(860)
Transfer of balance to OREO	(285)	(6)
Loans charged off	(413)	(803)
Recoveries	56	128
Balance, end of period	35,818	34,063
Allowance on loans individually evaluated for impairment	35	1,590
Allowance on loans collectively evaluated for impairment	35,783	32,473
Balance, end of period	3,020,071	2,580,727
Balance, end of period: Loans individually evaluated for impairment	27,271	33,952
Balance, end of period: Loans collectively evaluated for impairment	2,992,800	2,546,775
Balance, end of period: Loans acquired with deteriorated credit quality	50,503	15,292
Non-Covered Loans [Member] | Commercial Business [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	28,721	25,705
(Reversal of) Provision for credit losses	(646)	2,065
Transfer of balance to OREO
Loans charged off	(225)	(31)
Recoveries	188	31
Balance, end of period	28,038	27,770
Allowance on loans individually evaluated for impairment	116	202
Allowance on loans collectively evaluated for impairment	27,922	27,568
Balance, end of period	2,534,612	2,020,510
Balance, end of period: Loans individually evaluated for impairment	2,958	6,486
Balance, end of period: Loans collectively evaluated for impairment	2,531,654	2,014,024
Balance, end of period: Loans acquired with deteriorated credit quality	3,339	24,193
Non-Covered Loans [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	13,917	12,655
(Reversal of) Provision for credit losses	(1,374)	1,024
Transfer of balance to OREO	(7)
Loans charged off	(1,183)	(1,274)
Recoveries	618	604
Balance, end of period	11,971	13,009
Allowance on loans individually evaluated for impairment	41
Allowance on loans collectively evaluated for impairment	11,930	13,009
Balance, end of period	1,734,830	1,353,404
Balance, end of period: Loans individually evaluated for impairment	312	228
Balance, end of period: Loans collectively evaluated for impairment	1,734,518	1,353,176
Balance, end of period: Loans acquired with deteriorated credit quality	4,276	5,640
Non-Covered Loans [Member] | Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	2,125	897
(Reversal of) Provision for credit losses	418	(119)
Transfer of balance to OREO	(267)
Loans charged off	(241)	(163)
Recoveries	31	10
Balance, end of period	2,066	625
Allowance on loans individually evaluated for impairment	137	168
Allowance on loans collectively evaluated for impairment	1,929	457
Balance, end of period	301,289	263,003
Balance, end of period: Loans individually evaluated for impairment	1,058	1,186
Balance, end of period: Loans collectively evaluated for impairment	300,231	261,817
Balance, end of period: Loans acquired with deteriorated credit quality	383
Non-Covered Loans [Member] | Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period
(Reversal of) Provision for credit losses
Transfer of balance to OREO
Loans charged off
Recoveries
Balance, end of period
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment
Balance, end of period
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment
Balance, end of period: Loans acquired with deteriorated credit quality
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	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
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment	111,832	101,725
Balance, end of period	1,004,173	1,260,662
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment	1,004,173	1,260,662
Balance, end of period: Loans acquired with deteriorated credit quality	190,837	247,125
Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	100,871	69,175
(Reversal of) Provision for credit losses	29	1,386
Increase (Decrease) in FDIC loss share receivable	(23,001)	1,268
Transfer of balance to OREO	(9,729)	(3,179)
Loans charged off	(41)	(13,126)
Recoveries		14
Balance, end of period	68,129	55,538
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment	68,129	55,538
Balance, end of period	567,621	725,470
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment	567,621	725,470
Balance, end of period: Loans acquired with deteriorated credit quality	146,932	184,830
Covered Loans [Member] | Commercial Business [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	11,375	9,788
(Reversal of) Provision for credit losses		794
Increase (Decrease) in FDIC loss share receivable	(1,601)	728
Transfer of balance to OREO		(4)
Loans charged off
Recoveries
Balance, end of period	9,774	11,306
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment	9,774	11,306
Balance, end of period	87,032	104,102
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment	87,032	104,102
Balance, end of period: Loans acquired with deteriorated credit quality	2,832	4,005
Covered Loans [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	33,764	18,753
(Reversal of) Provision for credit losses		578
Increase (Decrease) in FDIC loss share receivable	(15,905)	529
Transfer of balance to OREO		(797)
Loans charged off		(9)
Recoveries		3
Balance, end of period	17,859	19,057
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment	17,859	19,057
Balance, end of period	172,192	194,539
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment	172,192	194,539
Balance, end of period: Loans acquired with deteriorated credit quality	22,685	27,596
Covered Loans [Member] | Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period
(Reversal of) Provision for credit losses
Increase (Decrease) in FDIC loss share receivable
Transfer of balance to OREO
Loans charged off
Recoveries
Balance, end of period
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment
Balance, end of period
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment
Balance, end of period: Loans acquired with deteriorated credit quality
Covered Loans [Member] | Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance, beginning of period	22,566	21,184
(Reversal of) Provision for credit losses		(2,011)
Increase (Decrease) in FDIC loss share receivable	(4,907)	(1,841)
Transfer of balance to OREO	(1,589)	(1,377)
Loans charged off		(131)
Recoveries
Balance, end of period	16,070	15,824
Allowance on loans individually evaluated for impairment
Allowance on loans collectively evaluated for impairment	16,070	15,824
Balance, end of period	177,328	236,551
Balance, end of period: Loans individually evaluated for impairment
Balance, end of period: Loans collectively evaluated for impairment	177,328	236,551
Balance, end of period: Loans acquired with deteriorated credit quality	$ 18,388	$ 30,694