Changes in Benefit Obligations and Plan Assets as Well as Funded Status of Retirement Plans (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number Of Indexed Funds | Investment	6
Change in plan assets
Fair value of plan assets at beginning of year	$ 759,551
Fair value of plan assets at end of year	825,806	$ 759,551
Pension Plan [Member]
Change in benefit obligation [Roll Forward]
Obligation at beginning of year	726,421	685,295
Service cost	13,372	12,895	$ 15,562
Interest cost	25,501	25,781	28,066
Actuarial losses	54,562	34,705
Acquisition	19,225	0
Special termination benefits	0	2,837	0
Plan amendments	147	472
Benefits paid	(43,598)	(33,492)
Curtailment gain	0	0
Participant contributions	0	0
Foreign currency exchange rate changes	12,519	(2,072)
Obligation at end of year	808,149	726,421	685,295
Change in plan assets
Fair value of plan assets at beginning of year	759,551	704,779
Actual return on plan assets	108,154	87,132
Employer contributions	1,699	1,132
Participant contributions	0	0
Benefits paid	(43,598)	(33,492)
Fair value of plan assets at end of year	825,806	759,551	704,779
Funded status	17,657	33,130
Amounts recognized in the consolidated balance sheets
Non-current assets	118,892	104,089
Current liabilities	(2,227)	(1,295)
Non-current liabilities	(99,008)	(69,664)
Net amount recognized	17,657	33,130
Amounts recognized in accumulated other comprehensive loss (income)
Net actuarial loss (gain)	154,642	148,941
Prior service cost (credit)	938	1,105
Net amount recognized	155,580	150,046
Other Postretirement Benefits Plan [Member]
Change in benefit obligation [Roll Forward]
Obligation at beginning of year	21,698	28,022
Service cost	104	222	444
Interest cost	692	891	1,281
Actuarial losses	630	641
Acquisition	0	0
Special termination benefits	0	0
Plan amendments	(2)	(5,636)
Benefits paid	(2,325)	(3,007)
Curtailment gain	0	(305)
Participant contributions	142	870
Foreign currency exchange rate changes	0	0
Obligation at end of year	20,939	21,698	28,022
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	2,183	2,137
Participant contributions	142	870
Benefits paid	(2,325)	(3,007)
Fair value of plan assets at end of year	0	0	$ 0
Funded status	(20,939)	(21,698)
Amounts recognized in the consolidated balance sheets
Non-current assets	0	0
Current liabilities	(2,083)	(2,502)
Non-current liabilities	(18,856)	(19,196)
Net amount recognized	(20,939)	(21,698)
Amounts recognized in accumulated other comprehensive loss (income)
Net actuarial loss (gain)	(5,561)	(6,787)
Prior service cost (credit)	(11,337)	(14,753)
Net amount recognized	$ (16,898)	$ (21,540)