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		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator [Abstract]
Net income	$ 48,231	$ 42,285	$ 135,697	$ 140,823
Denominator [Abstract]
Denominator for basic net income per common share (in shares)	177,455	183,085	178,040	185,515
Effect of dilutive securities:
Stock options	2,101	1,928	2,207	2,698
RSUs and deferred stock units	1,497	691	1,491	876
Denominator for diluted net income per common share (in shares)	181,053	185,704	181,738	189,089
Basic net income per common share (in dollars per share)	$ 0.27	$ 0.23	$ 0.76	$ 0.76
Diluted net income per common share (in dollars per share)	$ 0.27	$ 0.23	$ 0.75	$ 0.74