Loans and Allowances for Loan Losses - Changes in Carrying Amount of Covered Acquired Loans and Accretable Yield for Loans Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Covered loans [Member]
Financing Receivable, Impaired [Line Items]
Carrying Amount of Loans, Balance at beginning of period	$ 515,823	$ 671,443
Carrying Amount of Loans, Additions
Carrying Amount of Loans, Payments received, net	(48,448)	(200,719)
Carrying Amount of Loans, Accretion	9,601	45,099
Carrying Amount of Loans, Balance at end of period	476,976	515,823
Accretable Yield, Balance at beginning of period	115,594	153,137
Accretable Yield, Additions	0
Accretable Yield, Payments received, net	(72)
Accretable Yield, Accretion	(9,601)	(45,099)
Accretable Yield, Increase (decrease) in expected cash flows based on actual cash flow, loan sales and foreclosures assumptions	4,896	(19,326)
Accretable Yield, Net transfer from (to) nonaccretable difference to accretable yield	10,952	26,882
Accretable Yield, Balance at end of period	121,769	115,594
Non-Covered [Member]
Financing Receivable, Impaired [Line Items]
Carrying Amount of Loans, Balance at beginning of period	141,201	339,452
Carrying Amount of Loans, Additions
Carrying Amount of Loans, Payments received, net	(17,795)	(250,338)
Carrying Amount of Loans, Accretion	8,675	52,087
Carrying Amount of Loans, Balance at end of period	132,081	141,201
Accretable Yield, Balance at beginning of period	203,186	130,691
Accretable Yield, Additions	0
Accretable Yield, Payments received, net	(13,572)
Accretable Yield, Accretion	(8,675)	(52,087)
Accretable Yield, Increase (decrease) in expected cash flows based on actual cash flow, loan sales and foreclosures assumptions	7,723	23,688
Accretable Yield, Net transfer from (to) nonaccretable difference to accretable yield	(10,098)	100,894
Accretable Yield, Balance at end of period	$ 178,564	$ 203,186