Covered Loans - Summary of FDIC Loss Sharing Asset (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2015	Dec. 31, 2014
Covered Loans [Line Items]
Beginning balance	$ 88,513		$ 20,603
Cash received from FDIC	(15,989)
Ending balance	65,699	20,024	20,603
Adjustments Not Reflected in Income [Member]
Covered Loans [Line Items]
Cash received from FDIC	(15,989)
Other	518	389
Adjustments Reflected in Income [Member]
Covered Loans [Line Items]
(Amortization) accretion	(5,203)	(1,986)
Higher (lower) loan loss expectations	(412)
Write-downs/(gain) on sale of other real estate	$ (1,728)	$ 1,018