Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Plans [Member]
Components of Net Benefit Cost (Credit):
Service cost	$ 267	$ 315	$ 718	$ 938
Interest cost	7,636	6,744	22,807	20,193
Expected return on plan assets	(8,253)	(6,701)	(24,560)	(20,090)
Amortization of:
Prior service cost	708	708	2,176	2,114
Net actuarial loss (gain)	1,096	919	3,325	2,745
Net benefit cost (credit)	1,454	1,985	4,466	5,900
Medical Plan [Member]
Components of Net Benefit Cost (Credit):
Service cost	7	12	24	39
Interest cost	49	46	146	137
Expected return on plan assets
Amortization of:
Prior service cost
Net actuarial loss (gain)	(131)		(396)
Net benefit cost (credit)	$ (75)	$ 58	$ (226)	$ 176