Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ (6)	$ 606	$ 469	$ 1,951
Interest cost on projected benefit obligation	1,099	1,120	3,200	3,319
Expected return on plan assets	(1,444)	(1,772)	(4,337)	(5,385)
Amortization of prior service credit	29	(34)	(41)	(104)
Recognized net actuarial loss	638	586	1,708	1,521
Net Periodic Pension Expense	$ 316	$ 506	$ 999	$ 1,302