Schedule of Measurement Dates (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Benefit Obligation
Defined Benefit Plan Disclosure [Line Items]
Measurement Dates	Dec. 31, 2016	Dec. 31, 2015
Fair Value Of Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Measurement Dates	Dec. 31, 2016	Dec. 31, 2015