Net Income Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic:
Net income	$ 472,658	$ 440,065	$ 556,807
Basic weighted shares outstanding (in shares)	309,748,000	320,195,000	320,830,000
Net income per share (in dollars per share)	$ 1.53	$ 1.37	$ 1.74
Diluted:
Net income	$ 472,658	$ 440,065	$ 556,807
Basic weighted shares outstanding (in shares)	309,748,000	320,195,000	320,830,000
Stock options, ESPP and restricted stock unit shares (in shares)	2,149,000	2,823,000	3,667,000
Diluted weighted shares outstanding	311,897,000	323,018,000	324,497,000
Net income per share (in dollars per share)	$ 1.52	$ 1.36	$ 1.72
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	1,600,000	2,000,000	1,800,000