Assets Acquired in FDIC-Assisted Acquisitions - Rollforward of Acquired Covered Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Covered Loans [Line Items]
Balance, beginning of year	$ 25,493	$ 16,698
Accretion	22,188	42,208
Transfers to covered other real estate owned	(4,160)
Balance, end of year	15,578	25,493
Loans with Deterioration of Credit Quality [Member]
Covered Loans [Line Items]
Balance, beginning of year	390,237	507,712
Charge-offs, net of recoveries	(9,255)	(7,695)
Accretion	22,188	42,208
Transfers to covered other real estate owned	(13,650)	(31,833)
Transfer to purchased, non-covered loans due to loss share expiration	(15,475)
Payments received	(102,996)	(120,155)
Other	230
Balance, end of year	$ 271,279	$ 390,237