Employee Pension Benefits - Components of Net Periodic Pension Benefit of Pension Plan and Excess Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]
Interest cost	$ 360	$ 506	$ 1,178	$ 1,518
Expected return on assets	(1,316)	(1,311)	(4,083)	(3,935)
Recognized net actuarial loss	0	0	1	0
Amortization of prior service (credit)	(388)	(389)	(1,166)	(1,166)
Net periodic pension (benefit)	$ (1,344)	$ (1,194)	$ (4,070)	$ (3,583)