Net Income per Share (Schedule of Components Used in Diluted and Basic Income Per Common Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Numerator [Abstract]
Net income	$ 43,227	$ 50,617
Denominator [Abstract]
Denominator for basic net income per common share	178,120	186,849
Effect of dilutive securities:
Stock options	2,423	3,353
RSUs and deferred stock units	1,799	1,181
Denominator for diluted net income per common share	182,342	191,383
Basic net income per common share	$ 0.24	$ 0.27
Diluted net income per common share	$ 0.24	$ 0.26