Allowance for Credit Losses - Summary of Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Receivables [Abstract]
Allowance for non-covered loans	$ 110,374		$ 120,708
Allowance for covered loans	7,070		9,492
Total allowance for loan losses	117,444	121,844	130,200	129,854	132,870	133,802
Allowance for unfunded letters of credit	2,436		2,295
Total allowance for credit losses	$ 119,880		$ 132,495