Allowance for Credit Losses - Summary of Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for non-covered loans	$ 120,708	$ 120,274
Allowance for covered loans	9,492	13,528
Total allowance for loan losses	130,200	133,802	124,704
Allowance for unfunded letters of credit	2,295	2,383
Total allowance for credit losses	$ 132,495	$ 136,185