Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 474	$ 672
Interest cost on projected benefit obligation	1,065	1,100
Expected return on plan assets	(1,459)	(1,807)
Amortization of prior service credit	(35)	(35)
Recognized net actuarial loss	544	468
Net Periodic Pension Expense	$ 589	$ 398