Effect of Master Netting Arrangements on Presentation of Derivative Assets and Liabilities in Consolidated Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Sep. 30, 2016		Dec. 31, 2015
Derivative Financial Instruments, Liabilities
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities	$ 5,599		$ 4,322
Gross Amounts Offset in the Statement of Condition	5,386		3,986
Net Amounts of Liabilities Presented in the Statement of Condition	213		336
Financial Instruments	0		0
Cash Collateral Received	0		0
Net Amount	213		336
Derivative Financial Instruments, Assets
Derivatives, Fair Value [Line Items]
Gross Amounts Of Recognized Assets	14,467	[1]	5,743	[2]
Gross Amounts Offset in the Statement of Condition	2,864		1,024
Net Amounts of Assets Presented in the Statement of Condition	11,603		4,719
Financial Instruments	0		0
Cash Collateral Received	0		0
Net Amount	$ 11,603		$ 4,719

[1] Includes $2.7 million to purchase Treasury options.

[2] Includes $1.9 million to purchase Treasury options.