Derivative Financial Instruments (Derivative Asset and Liability Balance Sheet Offsetting) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Offsetting Assets [Line Items]
Net amount presented in the Statements of Financial Condition	$ 88,828	$ 51,298	$ 69,034
Derivative Liabilities
Net amount presented in the Statements of Financial Condition	87,948	45,019	65,198
Interest Rate Contract
Offsetting Assets [Line Items]
Gross Amounts Recognized	80,203	42,779	56,938
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	80,203	42,779	56,938
Offsetting Derivative Positions	958	753	614
Collateral Posted	0	0	0
Net Credit Exposure	79,245	42,026	56,324
Derivative Liabilities
Gross Amounts Recognized	80,113	42,458	57,429
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	80,113	42,458	57,429
Offsetting Derivative Positions	(958)	(753)	(614)
Collateral Posted	(79,155)	(41,705)	(54,410)
Net Credit Exposure	0	0	$ 2,405
Collateral posted which resulted in excess collateral with counterparties	$ 86,000	$ 45,500