Commitments and Contingencies - (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 3,964,357	$ 3,871,834
Standby Letters Of Credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	140,515	159,930
Commercial Letters Of Credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	4,048	3,087
Commitments To Extend Credit [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	509,209	318,001
Unfunded Commitments Under Existing Lines And Loans [Member]
Loss Contingencies [Line Items]
Total financial instruments with off-balance sheet risk	$ 3,310,585	$ 3,390,816