Derivative Financial Instruments (Derivative Asset and Liability Balance Sheet Offsetting) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Offsetting Assets [Line Items]
Net amount presented in the Statements of Financial Condition	$ 49,703	$ 56,394	$ 101,052
Derivative Liabilities
Net amount presented in the Statements of Financial Condition	37,651	39,839	100,912
Interest Rate Contract
Offsetting Assets [Line Items]
Gross Amounts Recognized	46,647	49,213	89,036
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	46,647	49,213	89,036
Offsetting Derivative Positions	(15,828)	(14,441)	(161)
Collateral Posted	(3,150)	(8,530)	0
Net Credit Exposure	27,669	26,242	88,875
Derivative Liabilities
Gross Amounts Recognized	35,343	37,665	90,892
Less: Amounts offset in the Statements of Financial Condition	0	0	0
Net amount presented in the Statements of Financial Condition	35,343	37,665	90,892
Offsetting Derivative Positions	(15,828)	(14,441)	(161)
Collateral Posted	(19,515)	(12,400)	(90,731)
Net Credit Exposure	0	$ 10,824	0
Collateral posted which resulted in excess collateral with counterparties	$ 21,000		$ 94,200