Commitments and Contingencies (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	$ 5,399,762	$ 5,031,030
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	128,985	133,294
Letter of Credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	46,497	45,742
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	$ 5,224,280	$ 4,851,994