Income Taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Comprehensive provision for income taxes (benefit) allocable to:
Net income	$ 6,466	$ (560)	$ 28,923	$ (1,052)
Other comprehensive income (loss):
Marketable securities	(2,800)	3,700	(5,300)	4,900
Currency translation	3,100	1,000	5,700	2,000
Interest rate swap	200	100	200	(300)
Total	7,300	4,500	30,500	6,600
Defined Benefit Pension Plans
Other comprehensive income (loss):
Defined benefit plans	400	400	1,100	1,300
OPEB
Other comprehensive income (loss):
Defined benefit plans	$ (100)	$ (100)	$ (100)	$ (200)