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, 2013	Mar. 31, 2012
Numerator [Abstract]
Net income	$ 71,487	$ 43,227
Denominator [Abstract]
Denominator for basic net income per common share (in shares)	177,899	178,120
Effect of dilutive securities:
Stock options	1,776	2,423
RSUs and deferred stock units	1,887	1,799
Denominator for diluted net income per common share (in shares)	181,562	182,342
Basic net income per common share (in dollars per share)	$ 0.40	$ 0.24
Diluted net income per common share (in dollars per share)	$ 0.39	$ 0.24