Accumulated Other Comprehensive Loss - Related Tax Effects Allocated to Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Before Tax Amount
Total other comprehensive income (loss), before tax amount	$ 7,956	$ (9,281)
Tax (Expense) Benefit
Total other comprehensive income (loss), tax	(346)	90
After Tax Amount
Cumulative translation adjustment, after tax amount	7,141	(3,234)	$ (4,572)
Total other comprehensive income (loss), after tax amount	7,610	(9,191)
Retirement Benefits Adjustment
Before Tax Amount
Net actuarial gain (loss) and prior service credit, before tax amount	1,072	(6,553)
Reclassification of actuarial loss and prior service cost to net income, before tax amount	(257)	507
Total recognized in other comprehensive income (loss)	815	(6,046)
Tax (Expense) Benefit
Net actuarial gain (loss) and prior service credit, tax	(258)	206
Reclassification of actuarial loss and prior service cost to net income, tax	(88)	(117)
Net unrealized loss, before tax amount, tax	(346)	89
After Tax Amount
Net actuarial gain (loss) and prior service credit, after tax amount	814	(6,347)
Reclassification of actuarial loss and prior service cost to net income, after tax amount	(345)	390
Net unrealized loss, before tax amount, after tax amount	469	(5,957)
Cumulative translation adjustment
Before Tax Amount
Cumulative translation adjustment, before tax amount	7,141	(3,235)
Tax (Expense) Benefit
Cumulative translation adjustment, tax	0	1
After Tax Amount
Cumulative translation adjustment, after tax amount	$ 7,141	$ (3,234)