Reconciliation of Total Segment Income from Operations to Consolidated Income Before Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Income from operations	$ 170,978	$ 138,369	$ 316,603	$ 279,006
Interest expense	(11,571)	(12,802)	(23,748)	(25,722)
Gain from sales of equity securities	15,952		15,952
Other income, net	1,107	1,632	2,454	2,839
Income before income taxes	$ 176,466	$ 127,199	$ 311,261	$ 256,123