Fair Value of Assets and Liabilities - Roll-Forward of the Consolidated Condensed Statement of Financial Condition Items (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 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 June 30,	306
Accretion of previous discounted amounts	8
Purchases, issuances and settlements, net	0	0
Transfers in and/or out of Level 3	0	0
Fair value, Ending balance	1,803	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