Commitments and Contingencies - (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 4,168,103	$ 3,947,337
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	135,601	139,789
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	9,252	6,535
Unused commitments to extend credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 4,023,250	$ 3,801,013