Fair Value of Assets and Liabilities - Roll-Forward of the Consolidated Condensed Statement of Financial Condition Items (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, Beginning balance	$ 1,489	$ 1,489
Change in unrealized losses included in other comprehensive income for assets and liabilities still held at September 30,	289
Accretion of previous discounted amounts	12
Purchases, issuances and settlements, net	0	0
Transfers in and/or out of Level 3	0	0
Fair value, Ending balance	1,790	1,489
Other Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases, issuances and settlements, net	0	0
Transfers in and/or out of Level 3	$ 0	$ 0