Postretirement Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	$ 158,594	$ 171,358
Interest cost	6,616	6,194	$ 6,651
Actuarial (gain) loss	19,251	(11,494)
Benefits paid	(7,962)	(7,464)
Benefit obligation at end of year	176,499	158,594	171,358
Fair value of plan assets at beginning of year	134,198	147,908
Actual return (loss) on plan assets	33,875	(11,558)
Employer contributions	312	5,312
Benefits paid	(7,962)	(7,464)
Fair value of plan assets at end of year	160,423	134,198	147,908
Over (Under) funded status at end of year	(16,076)	(24,396)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	20,006	24,048
Interest cost	554	565	592
Actuarial (gain) loss	1,045	(2,129)
Benefits paid	(592)	(1,255)
Foreign exchange impact	837	(1,223)
Benefit obligation at end of year	21,850	20,006	24,048
Fair value of plan assets at beginning of year	20,576	24,168
Actual return (loss) on plan assets	2,963	(1,583)
Employer contributions	476	494
Benefits paid	(592)	(1,254)
Foreign exchange impact	934	(1,249)
Fair value of plan assets at end of year	24,357	20,576	$ 24,168
Over (Under) funded status at end of year	$ 2,507	$ 570