Derivative Financial Instruments (Derivative Asset and Liability Balance Sheet Offsetting) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Derivative Assets
Gross Amounts Recognized	$ 89,036	$ 42,779	$ 36,747
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	89,036	42,779	36,747
Offsetting Derivative Positions	(161)	(753)	(1,896)
Collateral Posted	0	0	0
Net Credit Exposure	88,875	42,026	34,851
Derivative Liabilities
Gross Amounts Recognized	90,892	42,458	36,605
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	90,892	42,458	36,605
Offsetting Derivative Positions	(161)	(753)	(1,896)
Collateral Posted	(90,731)	(41,705)	(34,709)
Net Credit Exposure	0	0	0
Security Owned and Pledged as Collateral, Fair Value	$ 94,200	$ 45,500	$ 36,000