Assets Acquired in FDIC-Assisted Acquisitions - Rollforward of Acquired Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Covered Loans [Line Items]
Balance, beginning of year	$ 15,578	$ 25,493	$ 25,493
Accretion	4,466	9,767	22,188
Transfer to covered other real estate owned	(1,094)	(68)
Balance, end of year	12,965	16,091	15,578
Loans with Deterioration of Credit Quality [Member]
Covered Loans [Line Items]
Balance, beginning of year	271,279	390,237	390,237
Charge-offs	(2,812)	(4,326)	(9,255)
Accretion	4,466	9,767	22,188
Transfer to covered other real estate owned	(1,230)	(4,925)	(13,650)
Transfer to purchased, non-covered loans due to loss share expiration			(15,475)
Payments received	(25,958)	(18,070)	(102,996)
Other		11	230
Balance, end of year	$ 245,745	$ 372,694	$ 271,279