Pension Plans and Other Postretirement Benefits - Fair Values of Company's Pension Plan Assets by Asset Category (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Interest and dividend receivable on plan assets	$ 1,499,000	$ 2,047,000
Investment Grade Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in mutual funds	33.00%	55.00%
High-Yielding Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment in mutual funds	67.00%	45.00%