Employee Pension Benefits - Components of Net Periodic Pension Benefit of Pension Plan and Excess Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Interest cost	$ 409	$ 506
Expected return on assets	(1,383)	(1,312)
Recognized net actuarial loss	1	0
Amortization of prior service (credit)	(389)	(389)
Net periodic pension (benefit)	$ (1,362)	$ (1,195)