Retirement and Postretirement Benefits Other Than Pension Plans - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2015	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net settlement loss		$ (1,593)	$ (1,593)
Pension plan's assumed discount rate	4.00%			3.70%
Increase in pension plan liability			2,200
Expected long-term rate of return on plan assets	6.50%			7.50%
Corporate Operating Expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Net settlement loss		$ (1,600)	$ (1,600)