Employee Benefit Plans - Summary of the Amounts of Amortization Included in Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss (gain)	$ (448)
Amortization of prior service credit	(9,829)
Total	(10,277)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss (gain)	683
Total	683
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss (gain)	(1,131)
Amortization of prior service credit	(9,829)
Total	$ (10,960)