Retirement Plans - Components of Net Periodic Benefits Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Net Periodic Benefit Cost [Line Items]
Service cost	$ 3,425	$ 3,929
Interest cost	4,809	3,944
Expected return on plan assets	(8,061)	(6,263)
Amortization of prior service cost
Amortization of net loss	8	1,745
Amortization of transition obligation
Net periodic benefit cost	181	3,355
Other Post-retirement Benefits [Member]
Defined Benefit Plan Net Periodic Benefit Cost [Line Items]
Service cost	37	55
Interest cost	338	330
Expected return on plan assets
Amortization of prior service cost
Amortization of net loss	157	38
Amortization of transition obligation
Net periodic benefit cost	$ 532	$ 423