Pension and Other Employee Benefits - Reconciliation of Benefit Obligation, Fair Value of Plan Assets and Funded Status of Respective Defined Benefit (Pension) and Postretirement Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets:
Employer contributions		$ 5,200	$ 4,100	$ 2,800
Amounts recognized in the balance sheet consist of:
Total non-current liabilities		31,976	25,038
Pension Benefits [Member]
Change in benefit obligation:
Obligation at beginning of period	$ 43,075	43,075	48,844
Acquired benefit obligation		40,135	0
Service cost		265	232
Interest cost		494	1,371
Employee contributions		39	0
Settlement transfer to third party		(18,084)	(7,438)
Actuarial (gains) losses		954	(36)
Foreign exchange effect		(1,314)	3,112
Benefits paid		(2,376)	(3,010)
Obligation at end of period		63,188	43,075	48,844
Change in plan assets:
Fair value of plan assets, beginning of period	18,037	18,037	25,153
Acquired plan assets		31,331	0
Settlement transfer to third party		(17,927)	(7,438)
Actual return on plan assets		147	1,844
Employer contributions		153	98
Employee contributions		39	0
Foreign exchange effect		251	0
Plan expenses		0	(119)
Benefits paid		(819)	(1,501)
Fair value of plan assets, end of period		31,212	18,037	25,153
Unfunded status		31,976	25,038
Amounts recognized in the balance sheet consist of:
Total non-current liabilities		31,976	25,038
Pension Benefits [Member] | US Plan [Member]
Change in benefit obligation:
Obligation at beginning of period	18,084	18,084	25,644
Acquired benefit obligation		0	0
Service cost		0	3
Interest cost		0	948
Employee contributions		0	0
Settlement transfer to third party		(18,084)	(7,438)
Actuarial (gains) losses		0	168
Foreign exchange effect		0	0
Benefits paid		0	(1,241)
Obligation at end of period		0	18,084	25,644
Change in plan assets:
Fair value of plan assets, beginning of period	17,927	17,927	24,931
Acquired plan assets		0	0
Settlement transfer to third party	(18,700)	(17,927)	(7,438)
Actual return on plan assets		0	1,823
Employer contributions		0	0
Employee contributions		0	0
Foreign exchange effect		0	0
Plan expenses		0	(148)
Benefits paid		0	(1,241)
Fair value of plan assets, end of period		0	17,927	24,931
Unfunded status		0	157
Amounts recognized in the balance sheet consist of:
Total non-current liabilities		0	157
Pension Benefits [Member] | Non-U.S. Plans [Member]
Change in benefit obligation:
Obligation at beginning of period	24,991	24,991	23,200
Acquired benefit obligation		40,135	0
Service cost		265	229
Interest cost		494	423
Employee contributions		39	0
Settlement transfer to third party		0	0
Actuarial (gains) losses		954	(204)
Foreign exchange effect		(1,314)	3,112
Benefits paid		(2,376)	(1,769)
Obligation at end of period		63,188	24,991	23,200
Change in plan assets:
Fair value of plan assets, beginning of period	$ 110	110	222
Acquired plan assets		31,331	0
Settlement transfer to third party		0	0
Actual return on plan assets		147	21
Employer contributions		153	98
Employee contributions		39	0
Foreign exchange effect		251	0
Plan expenses		0	29
Benefits paid		(819)	(260)
Fair value of plan assets, end of period		31,212	110	$ 222
Unfunded status		31,976	24,881
Amounts recognized in the balance sheet consist of:
Total non-current liabilities		$ 31,976	$ 24,881