Allowance for Credit Losses - Summary of Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Allowance for non-covered loans	$ 101,760		$ 106,547
Allowance for covered loans	678		7,070
Total allowance for loan losses	102,438	103,053	113,617	112,585	117,444	130,200
Allowance for unfunded letters of credit	2,121		3,495
Total allowance for credit losses	$ 104,559		$ 117,112