Employee Benefit Plans (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) participant	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cost recognized	$ 1,032	$ 1,029	$ 1,004
Requisite service period	5 years
Effect of one percentage point increase in assumed health care costs, affect on accumulated benefit obligation	$ 159
Effect of one percentage point decrease in assumed health care costs, effect on accumulated benefit obligation	(149)
Effect of one percentage point increase in assumed health care costs, affect on service and interest cost	200
Effect of one percentage point decrease in assumed health care costs, affect on service and interest cost	$ (185)
Effect On Accumulated Benefit Obligation And Service And Interest Cost [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Ultimate trend rate (as a percent)	1.00%
Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	60.00%
Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	30.00%
Other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	10.00%
Debt Category Concentration [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	10.00%
Post-Employment Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of participants | participant	211
Number of active participants eligible for benefits | participant	29
Minimum age of participant to become eligible for benefits	62 years
Age up to which health benefits continuation paid	65 years
Expected contributions in next fiscal year, net of Medicare Part D subsidy receipts	$ 545
Post-Employment Benefit Plan [Member] | Medicare Part D Subsidy Receipts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Medicare Part D subsidy receipts to the plan in 2016	$ 22
Minimum [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	80.00%
Minimum [Member] | Percentage Variance From Established Investment Category Targets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target plan asset allocations (as a percent)	10.00%