Commitments and Contingencies (Outstanding Financial Instruments Contract Amounts Represent Credit Risk) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	$ 5,031,030	$ 4,547,484
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	133,294	142,964
Letter of Credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	45,742	27,787
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Total credit-related financial instruments with off-balance sheet risk	$ 4,851,994	$ 4,376,733