Securities - Trading Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	$ 7,545	$ 7,150
Corporate equity securities
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	5,398	5,125
Mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	1,626	1,499
Corporate notes and bonds
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	248	254
U.S. Gov’t sponsored entities
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	51	52
Certificates of deposit
Debt and Equity Securities, FV-NI [Line Items]
Trading securities	$ 222	$ 220