Acquired Loans and Covered Loans (Detail) - Changes in FDIC Indemnification Asset (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
FDIC Indemnification Asset [Roll Forward]
Balance at the beginning of the year	$ 16,585	$ 37,051	$ 65,609
Amortization	(3,315)	(2,984)	(14,098)
Change in expected reimbursements from the FDIC for changes in expected credit losses	(481)	(1,242)	3,338
Payments received from the FDIC	(4,337)	(16,240)	(17,798)
Balance at the end of the year	$ 8,452	$ 16,585	$ 37,051