Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Obligations [Member]
Components of net periodic benefit cost:
Service cost	$ 5,554	$ 5,423	$ 5,863
Interest cost	9,310	10,510	11,687
Expected return on plan assets	(11,066)	(11,112)	(11,170)
Amortization of prior service credit	(54)	(55)	(63)
Net loss recognition	6,388	5,974	6,030
Net periodic benefit cost	10,132	10,740	12,347
Other Postretirement Obligations [Member]
Components of net periodic benefit cost:
Service cost	125	116	92
Interest cost	1,910	2,077	2,199
Amortization of prior service credit	(108)	(111)	(116)
Net loss recognition	932	842	386
Net periodic benefit cost	$ 2,859	$ 2,924	$ 2,561