Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Plans [Member]
Components of Net Periodic Benefit Cost (Credit):
Service cost	$ 314	$ 353	$ 621	$ 713
Interest cost	5,246	6,153	10,459	12,259
Expected return on plan assets	(7,233)	(7,019)	(14,399)	(14,090)
Amortization of:
Prior service cost	604	591	1,194	1,194
Net actuarial loss (gain)	1,012	1,137	2,001	2,283
Net periodic benefit cost (credit)	(57)	1,215	(124)	2,359
Medical Plan [Member]
Components of Net Periodic Benefit Cost (Credit):
Service cost	2	5	6	13
Interest cost	38	41	83	90
Amortization of:
Net actuarial loss (gain)	(92)		(92)
Net periodic benefit cost (credit)	$ (52)	$ 46	$ (3)	$ 103