Components of Other Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Other Income [Line Items]
Investment income	$ 10,692	$ 6,684	$ 25,969	$ 13,875
Interest income	577	663	2,281	1,534
Gain (loss) on sale of fixed assets	2,266	(7)	2,240	(45)
Forfeiture of vested stock options	3,005	0	3,005	0
Other	877	256	1,202	(204)
Other income, net	$ 17,417	$ 7,596	$ 34,697	$ 15,160