Defined Benefit Pension Plan and Postretirement Benefits - Post-Retirement Benefit Obligation and Unrealized Gain (Losses) (Detail) - Split-Dollar Life Insurance Arrangement [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefit obligation	$ 25	$ 46
Unrealized gains (losses) in AOCI	$ 386	$ 342