Assets Acquired in FDIC-Assisted Acquisitions - Rollforward of Acquired Covered Loans (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Covered Loans [Line Items]
Balance, beginning of year	$ 15,578	$ 25,493	$ 25,493
Accretion	6,251	15,432	22,188
Transfer to covered other real estate owned	(2,039)	(1,425)
Transfer to purchased, non-covered loans due to loss-share expiration	(84)
Balance, end of year	12,060	15,911	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	(7,065)	(5,694)	(9,255)
Accretion	6,251	13,330	22,188
Transfer to covered other real estate owned	(6,534)	(9,083)	(13,650)
Transfer to purchased, non-covered loans due to loss-share expiration	(15,462)		(15,475)
Payments received	(38,871)	(57,540)	(102,996)
Other			230
Balance, end of year	$ 209,598	$ 331,250	$ 271,279