Pension Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Components of net periodic benefit cost
Service cost	$ 85	$ 74	$ 170	$ 148
Interest cost	48	35	96	70
Expected return on assets	(94)	(83)	(188)	(166)
Amortization of prior service cost and net loss	(12)	(15)	(24)	(30)
Pension expense	$ 27	$ 11	$ 54	$ 22