Net Periodic Benefit Cost for Defined Benefit Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 431	$ 234	$ 1,319	$ 761
Interest cost	33	40	102	119
Expected return on plan assets	(24)	(34)	(73)	(101)
Amortization of prior service cost	82	37	(336)	110
Net periodic benefit cost	$ 522	$ 277	$ 1,012	$ 889