Loans and Allowance for Loan Losses - Changes in Carrying Amount of Covered Acquired Loans and Accretable Yield for Loans Receivable (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Carrying Amount of Loans, Balance at beginning of period	$ 358,666	$ 515,823
Carrying Amount of Loans, Additions
Carrying Amount of Loans, Payments received, net	(92,890)	(189,987)
Carrying Amount of Loans, Accretion	15,054	32,830
Carrying Amount of Loans, Balance at end of period	280,830	358,666
Accretable Yield, Balance at beginning of period	122,715	115,594
Accretable Yield, Additions
Accretable Yield, Payments received, net	(953)	(1,298)
Accretable Yield, Accretion	(15,054)	(32,830)
Accretable Yield, Increase (Decrease) in expected cash flows based on actual cash flows and changes in cash flow assumptions	1,783	(17,433)
Net transfers from nonaccretable difference to accretable yield	11,917	58,682
Accretable Yield, Balance at end of period	120,408	122,715
Non-Covered [Member]
Financing Receivable, Impaired [Line Items]
Carrying Amount of Loans, Balance at beginning of period	68,075	141,201
Carrying Amount of Loans, Additions
Carrying Amount of Loans, Payments received, net	(47,979)	(116,187)
Carrying Amount of Loans, Accretion	35,741	43,061
Carrying Amount of Loans, Balance at end of period	55,837	68,075
Accretable Yield, Balance at beginning of period	131,370	203,186
Accretable Yield, Additions
Accretable Yield, Payments received, net	(28,487)	(47,330)
Accretable Yield, Accretion	(35,741)	(43,061)
Accretable Yield, Increase (Decrease) in expected cash flows based on actual cash flows and changes in cash flow assumptions	(380)	3,894
Net transfers from nonaccretable difference to accretable yield	19,076	14,681
Accretable Yield, Balance at end of period	$ 85,838	$ 131,370