Allowance for Credit Losses - Summary of Provision for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Provision for non-covered loans									$ 9,317	$ 17,171	$ 25,640
Provision for covered loans									(5,872)	(2,276)	0
Total provision for loan losses									3,445	14,895	25,640
Provision for unfunded letters of credit									(1,561)	1,200	(88)
Total provision for credit losses	$ 3,980	$ (423)	$ (5,671)	$ 3,998	$ 6,440	$ 5,334	$ 2,552	$ 1,769	$ 1,884	$ 16,095	$ 25,552