Credit Risk Portfolio Based On Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	$ 6,010,681	$ 5,686,749	$ 5,144,766
Commercial - credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	118,613	104,320
Commercial - credit card [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	118,529	104,259
Commercial - credit card [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	84	61
Real estate - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	229,492	212,363
Real estate - residential [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	228,715	211,697
Real estate - residential [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	777	666
Real estate - Home Equity Line of Credit [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	562,765	573,923
Real estate - Home Equity Line of Credit [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	562,506	573,698
Real estate - Home Equity Line of Credit [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	259	225
Consumer - credit card [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	314,147	334,518
Consumer - credit card [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	312,307	332,233
Consumer - credit card [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	1,840	2,285
Consumer - other [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	51,070	54,550
Consumer - other [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	49,809	53,239
Consumer - other [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	1,261	1,311
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	19,901	19,084	7,799
Leases [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity	19,901	19,084
Leases [Member] | Non-performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit Risk Profile Based on Payment Activity