Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic earnings (loss) per share:
Net (loss) income	$ (1,862)	$ 96,351	$ 157,130	$ 314,507
Weighted average common shares outstanding	34,422,553	36,288,596	34,517,552	36,746,881
Basic (loss) earnings per share	$ (0.05)	$ 2.66	$ 4.55	$ 8.56
Diluted earnings (loss) per share:
Net (loss) income	$ (1,862)	$ 96,351	$ 157,130	$ 314,507
Weighted average common shares outstanding	34,422,553	36,288,596	34,517,552	36,746,881
Share equivalents:
Options	0	440,811	493,225	413,702
Restricted stock units and performance-based equity awards	0	460,315	304,529	234,976
Employee share purchase plan	0	0	1,289	0
Weighted average common shares and common share equivalents outstanding - diluted	34,422,553	37,189,722	35,316,595	37,395,559
Diluted (loss) earnings per share	$ (0.05)	$ 2.59	$ 4.45	$ 8.41