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	Mar. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefit obligation	$ 10	$ 12
Unrealized gains (losses) in AOCI	$ 35	$ 40