Postretirement Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	$ 171,358	$ 162,727
Interest cost	6,194	6,651	$ 6,934
Actuarial (gain) loss	(11,494)	9,109
Benefits paid	(7,464)	(7,129)
Benefit obligation at end of year	158,594	171,358	162,727
Fair value of plan assets at beginning of year	147,908	137,092
Actual return (loss) on plan assets	(11,558)	15,533
Employer contributions	5,312	2,412
Benefits paid	(7,464)	(7,129)
Fair value of plan assets at end of year	134,198	147,908	137,092
Over (Under) funded status at end of year	(24,396)	(23,450)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	24,048	22,034
Interest cost	565	592	733
Actuarial (gain) loss	(2,129)	(156)
Benefits paid	(1,255)	(516)
Foreign exchange impact	(1,223)	2,094
Benefit obligation at end of year	20,006	24,048	22,034
Fair value of plan assets at beginning of year	24,168	20,336
Actual return (loss) on plan assets	(1,583)	1,957
Employer contributions	494	365
Benefits paid	(1,254)	(516)
Foreign exchange impact	(1,249)	2,026
Fair value of plan assets at end of year	20,576	24,168	$ 20,336
Over (Under) funded status at end of year	$ 570	$ 120