Pension Expense (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
Service cost	$ 78	$ 85	$ 156	$ 170
Interest cost	50	48	100	96
Expected return on assets	(86)	(94)	(172)	(188)
Amortization of prior service cost and net loss	(2)	(12)	(4)	(24)
Pension expense	$ 40	$ 27	$ 80	$ 54