Components of Net Periodic Pension Benefit Costs (Detail) (Pension Benefits, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,676	$ 3,740	$ 7,399	$ 7,510
Interest cost	6,920	7,144	13,829	14,314
Expected return on plan assets	(11,801)	(10,186)	(22,314)	(20,400)
Amortization of prior service cost	477	510	953	1,021
Amortization of actuarial losses	3,088	1,993	6,176	3,985
Net periodic benefit cost	$ 2,360	$ 3,201	$ 6,043	$ 6,430