Income Taxes - Component of Income Taxes Expenses (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Line Items]
Expected tax provision (benefit) at U.S. federal statutory income tax rate of 35%	$ (3,100,000)	$ 3,800,000	$ (15,900,000)	$ 25,200,000
Incremental U.S. tax and rate differences on equity in earnings		(1,700,000)	(7,400,000)	(7,600,000)
Nontaxable income	(100,000)	(100,000)	(800,000)	(800,000)
U.S. state income taxes and other, net	100,000	100,000	300,000	600,000
Total	(3,145,000)	2,097,000	(23,827,000)	17,426,000
Comprehensive provision (benefit) for income taxes allocable to:
Continuing operations	(3,145,000)	2,097,000	(23,827,000)	17,426,000
Discontinued operations		1,000,000		2,500,000
Other comprehensive income (loss):
Marketable securities	32,100,000	(300,000)	38,500,000	(42,600,000)
Currency translation	2,200,000	4,400,000	(100,000)	2,000,000
Total	31,500,000	7,500,000	15,500,000	(20,000,000)
Defined Benefit Pension Plans
Other comprehensive income (loss):
Defined benefit plans	400,000	300,000	1,100,000	900,000
OPEB
Other comprehensive income (loss):
Defined benefit plans	$ (100,000)		$ (200,000)	$ (200,000)