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		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator [Abstract]
Net income	$ 47,921	$ 38,123	$ 98,538	$ 79,001
Add back of interest expense on 1% convertible senior notes (net of tax)	0	396	0	818
Numerator for diluted net income per common share	$ 47,921	$ 38,519	$ 98,538	$ 79,819
Denominator [Abstract]
Denominator for basic net income per common share	186,612	173,317	186,731	172,209
Effect of dilutive securities:
Stock options	2,810	3,992	3,081	3,717
Effect of escrow contingencies	0	339	0	339
RSUs and deferred stock units	757	1,396	969	1,299
Assumed conversion of 1% convertible senior notes	0	11,435	0	12,182
Denominator for diluted net income per common share	190,179	190,479	190,781	189,746
Basic net income per common share	$ 0.26	$ 0.22	$ 0.53	$ 0.46
Diluted net income per common share	$ 0.25	$ 0.20	$ 0.52	$ 0.42