Employer Sponsored Benefit Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Components of net periodic benefit cost
Interest cost	$ 535	$ 517	$ 1,070	$ 1,033
Expected return on assets	(605)	(590)	(1,210)	(1,180)
Amortization of actuarial loss	234	224	467	449
Net periodic benefit cost	$ 164	$ 151	$ 327	$ 302