Employer Sponsored Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Components of net periodic benefit cost
Interest cost	$ 535	$ 517	$ 1,605	$ 1,550
Expected return on assets	(605)	(590)	(1,815)	(1,770)
Amortization of actuarial loss	233	224	700	673
Net periodic benefit cost	$ 163	$ 151	$ 490	$ 453