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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Numerator [Abstract]
Net income	$ 44,239	$ 47,921	$ 87,466	$ 98,538
Denominator [Abstract]
Denominator for basic net income per common share (in shares)	178,547	186,612	178,333	186,731
Effect of dilutive securities:
Stock options	2,092	2,810	2,259	3,081
RSUs and deferred stock units	1,178	757	1,488	969
Denominator for diluted net income per common share (in shares)	181,817	190,179	182,080	190,781
Basic net income per common share (in dollars per share)	$ 0.25	$ 0.26	$ 0.49	$ 0.53
Diluted net income per common share (in dollars per share)	$ 0.24	$ 0.25	$ 0.48	$ 0.52