Commitments and Contingencies - Outstanding Financial Instruments Contract Amounts Represent Credit Risk (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 4,563,478	$ 4,276,471
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	146,689	135,761
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	26,025	13,621
Unused commitments to extend credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 4,390,764	$ 4,127,089