Significant Unobservable Inputs in Estimation of Fair Value (Detail) - Level 3 - Absolute Return Funds - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Pension and Other Postretirement Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Fair value of plan assets at beginning of year		$ 32,411
Total gains or losses (realized and unrealized)	$ 1,773	553
Sales	(5,000)	(4,000)
Fair value of plan assets at end of year	$ 25,737	$ 28,964