Pension Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Components of net periodic benefit cost
Service cost	$ 85	$ 74	$ 255	$ 222
Interest cost	48	35	144	105
Expected return on assets	(94)	(83)	(282)	(249)
Amortization of prior service cost and net loss	(12)	(15)	(36)	(45)
Pension expense	$ 27	$ 11	$ 81	$ 33