Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Net Periodic Pension Cost
Service cost-benefits earned during the period	$ 2,601	$ 2,369	$ 2,767
Interest cost on projected benefit obligation	4,425	4,470	3,985
Expected return on plan assets	(7,180)	(6,907)	(6,207)
Amortization of prior service cost (credit)	(138)	(137)	(138)
Recognized net actuarial loss	2,028	941	2,425
Net Periodic Pension Expense	1,736	736	2,832
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss)
Net actuarial loss (gain)	5,678	13,294	(15,499)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Actuarial Gain (Loss), before Tax	2,028	941	2,425
Recognized prior service credit	138	137	138
Total (Before Tax Effects)	3,788	12,490	(17,786)
Total Recognized in Net Benefit Cost and Other Comprehensive Income (Loss) (Before Tax Effects)	$ 5,524	$ 13,226	$ (14,954)