Stockholders' Equity (Schedule Of Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Gain Loss On Investments By Category [Line Items]
Net (loss) income	$ 51,845	$ 21,928	$ 9,053	$ (108,971)	$ 17,504	$ 30,534	$ 18,395	$ 26,298	$ (26,145)	$ 92,731	$ 76,928
Unrealized (loss) gain on marketable securities, net of tax									(124)	(220)	235
Less: reclassification adjustment for net (gains) losses included in net income, net of tax										(60)	34
Comprehensive income (loss)									(26,269)	92,511	77,163
Categories of Investments, Marketable Securities, Available-for-sale Securities [Member]
Gain Loss On Investments By Category [Line Items]
Unrealized (loss) gain on marketable securities, net of tax									$ (124)	$ (160)	$ 201