Changes in Benefit Obligations and Plan Assets as Well as Funded Status of Retirement Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in plan assets
Fair value of plan assets at end of year	$ 633,261	$ 509,877
Pension Benefits
Change in benefit obligation
Obligation at beginning of year	609,738	541,443
Service cost	14,788	13,857	13,428
Interest cost	27,363	28,519	28,200
Actuarial losses (gains)	49,067	52,417
Plan amendments	(1,269)	(144)
Benefits paid	(28,301)	(24,973)
Curtailment gain		(449)
Foreign currency exchange rate changes	986	(932)
Obligation at end of year	672,372	609,738	541,443
Change in plan assets
Fair value of plan assets at beginning of year	509,877	494,181
Actual return on plan assets	74,774	39,782
Employer contributions	76,911	887
Benefits paid	(28,301)	(24,973)
Fair value of plan assets at end of year	633,261	509,877	494,181
Funded status	(39,111)	(99,861)
Amounts recognized in the consolidated balance sheets
Non-current assets	25,548
Current liabilities	(1,061)	(916)
Non-current liabilities	(63,598)	(98,945)
Net amount recognized	(39,111)	(99,861)
Amounts recognized in accumulated other comprehensive (loss) income
Net actuarial loss	175,763	166,722
Prior service cost (credit)	3,843	6,203
Net amount recognized	179,606	172,925
Other Postretirement Benefits
Change in benefit obligation
Obligation at beginning of year	51,131	54,452
Service cost	830	862	918
Interest cost	2,051	2,441	2,782
Actuarial losses (gains)	(1,299)	(703)
Plan amendments	(504)	(408)
Benefits paid	(3,904)	(4,436)
Curtailment gain		(1,909)
Participants' contributions	872	832
Obligation at end of year	49,177	51,131	54,452
Change in plan assets
Employer contributions	3,032	3,604
Participants' contributions	872	832
Benefits paid	(3,904)	(4,436)
Funded status	(49,177)	(51,131)
Amounts recognized in the consolidated balance sheets
Current liabilities	(3,941)	(4,311)
Non-current liabilities	(45,236)	(46,820)
Net amount recognized	(49,177)	(51,131)
Amounts recognized in accumulated other comprehensive (loss) income
Net actuarial loss	4,994	6,304
Prior service cost (credit)	(15,576)	(17,688)
Net amount recognized	$ (10,582)	$ (11,384)