Net Income per Share (Schedule of Components Used in Diluted and Basic Income Per Common Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Numerator [Abstract]
Net income	$ 42,285	$ 39,709	$ 140,823	$ 118,710
Add back of interest expense on 1% convertible senior notes (net of taxes)	0	146	0	964
Numerator for diluted net income per common share	$ 42,285	$ 39,855	$ 140,823	$ 119,674
Denominator [Abstract]
Denominator for basic net income per common share	183,085	181,457	185,515	175,292
Effect of dilutive securities:
Stock options	1,928	3,988	2,698	3,807
Effect of escrow contingencies	0	339	0	339
RSUs and deferred stock units	691	1,399	876	1,332
Assumed conversion of 1% convertible senior notes	0	4,088	0	9,484
Denominator for diluted net income per common share	185,704	191,271	189,089	190,254
Basic net income per common share	$ 0.23	$ 0.22	$ 0.76	$ 0.68
Diluted net income per common share	$ 0.23	$ 0.21	$ 0.74	$ 0.63