Employee Pension Benefits - Components of Net Periodic Pension Benefit of Pension Plan and Excess Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Compensation and Retirement Disclosure [Abstract]
Interest cost	$ 409	$ 506	$ 818	$ 1,012
Expected return on assets	(1,384)	(1,312)	(2,767)	(2,624)
Recognized net actuarial loss	0	0	1	0
Amortization of prior service (credit)	(389)	(388)	(778)	(777)
Net periodic pension (benefit)	$ (1,364)	$ (1,194)	$ (2,726)	$ (2,389)