Commitments and Contingencies - Summary of Financial Instruments with Off-Balance Sheet Risk (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Commitments to sell loans	$ 100,400	$ 85,000
Standby letters of credit [Member]
Financial instruments with off-balance sheet risk	228,694	237,279
Commercial letters of credit [Member]
Commercial letters of credit	6,043	11,076
Commercial loans [Member] | Commitments to Extend Credit [Member]
Financial instruments with off-balance sheet risk	1,944,815	1,778,837
Commercial loans [Member] | Loan Origination Commitments [Member]
Financial instruments with off-balance sheet risk	253,235	237,921
Home equity [Member] | Unused lines of credit [Member]
Financial instruments with off-balance sheet risk	620,397	570,247
Residential [Member] | Loan Origination Commitments [Member]
Financial instruments with off-balance sheet risk	247,275	275,116
Credit card [Member] | Unused lines of credit [Member]
Financial instruments with off-balance sheet risk	$ 59,969	$ 64,144