Defined Benefit Pension Plan and Postretirement Benefits - Post-Retirement Benefit Obligation and Unrealized Gain (Losses) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefit obligation	$ 3,409	$ 3,100	$ 2,481
Split-Dollar Life Insurance Arrangement [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefit obligation	37	46
Unrealized gains (losses) in AOCI	$ 267	$ 342