Postretirement Benefits Other Than Pensions - Schedule of Postretirement Benefit Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Funded status of the plans	$ 405
Domestic Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations at beginning of year	33,877	$ 33,955
Service cost	314	361	$ 434
Interest cost	1,297	1,383	1,411
Actuarial loss (gain)	1,021	112
Benefits paid	(1,690)	(1,939)
Other	5	5	25
Foreign currency exchange rate effect	0	0
Benefit obligation at end of year	34,824	33,877	33,955
Funded status of the plans	(34,824)	(33,877)
Net amount recognized at December 31	(34,824)	(33,877)
Foreign Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations at beginning of year	18,350	16,455
Service cost	423	372	380
Interest cost	693	678	678
Actuarial loss (gain)	4,002	926
Benefits paid	(651)	(601)
Other	0	0	0
Foreign currency exchange rate effect	1,425	520
Benefit obligation at end of year	24,242	18,350	$ 16,455
Funded status of the plans	(24,242)	(18,350)
Net amount recognized at December 31	$ (24,242)	$ (18,350)