Off-Balance Sheet Arrangements, Guarantees and Other Commitments Summary of Commercial and Standby Letters of Credit (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Expires In One Year or Less	$ 1,386,497
Expires After One Year	92,667
Total Amount Outstanding	1,479,164	$ 1,254,338
Maximum Amount of Future Payments	1,479,164
Standby Letter of Credit
Guarantor Obligations [Line Items]
Securities Collateral Available To Reimburse Letter Of Credit Losses	500
Deferred Revenue	10,000	$ 8,000
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	1,324,632
Expires After One Year	85,790
Total Amount Outstanding	1,410,422
Maximum Amount of Future Payments	1,410,422
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	56,599
Expires After One Year	6,877
Total Amount Outstanding	63,476
Maximum Amount of Future Payments	63,476
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires In One Year or Less	5,266
Expires After One Year	0
Total Amount Outstanding	5,266
Maximum Amount of Future Payments	$ 5,266