Securities - Trading Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 4,858	$ 4,576
Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	3,312	3,389
Mutual Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	1,037	750
Corporate Notes and Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	254	130
U.S. Government Sponsored Entities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	53	54
Certificates of Deposit [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 202	$ 253