Employee Benefit Plans - Composition of Pension Plan Assets by Fair Value Level (Detail) - Defined Benefit Pension Plans - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total	$ 40,626	$ 44,222	$ 42,268
United States
Defined Benefit Plan Disclosure [Line Items]
Total	30,122	32,360
U.K.
Defined Benefit Plan Disclosure [Line Items]
Total	10,504	11,862
Equities | United States
Defined Benefit Plan Disclosure [Line Items]
Total	11,353
CMRT | United States
Defined Benefit Plan Disclosure [Line Items]
Total	1,663	32,360
Fixed Income | United States
Defined Benefit Plan Disclosure [Line Items]
Total	13,856
Other | U.K.
Defined Benefit Plan Disclosure [Line Items]
Total	10,504	11,862
Cash and Other | United States
Defined Benefit Plan Disclosure [Line Items]
Total	3,250
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total	30,130	11,862
Level 1 | Equities | United States
Defined Benefit Plan Disclosure [Line Items]
Total	3,423
Level 1 | Fixed Income | United States
Defined Benefit Plan Disclosure [Line Items]
Total	13,856
Level 1 | Other | U.K.
Defined Benefit Plan Disclosure [Line Items]
Total	10,504	11,862
Level 1 | Cash and Other | United States
Defined Benefit Plan Disclosure [Line Items]
Total	2,347
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total		32,360
Level 2 | CMRT | United States
Defined Benefit Plan Disclosure [Line Items]
Total		$ 32,360
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total	1,663
Level 3 | CMRT | United States
Defined Benefit Plan Disclosure [Line Items]
Total	1,663
Assets Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Total	8,833
Assets Measured at NAV | Equities | United States
Defined Benefit Plan Disclosure [Line Items]
Total	7,930
Assets Measured at NAV | Cash and Other | United States
Defined Benefit Plan Disclosure [Line Items]
Total	$ 903