Segment Information (Reconciliation of Total Segment Income from Operations to Consolidated Income before Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting [Abstract]
Income from operations	$ 142,517	$ 117,331	$ 459,120	$ 396,337
Interest expense	(11,934)	(12,727)	(35,682)	(38,449)
Debt retirement costs	(7,082)	0	(7,082)	0
Gain from sales of equity securities	477	0	16,429	0
Other income, net	1,222	1,457	3,676	4,296
Income before income taxes	$ 125,200	$ 106,061	$ 436,461	$ 362,184