Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income	$ 55,925	$ 47,532	$ 188,087	$ 156,495
Denominator:
Denominator for basic earnings per share - weighted-average shares outstanding	160,359	164,229	160,359	172,622
Effect of dilutive employee stock awards	1,418	1,484	1,357	1,401
Denominator for diluted earnings per share - weighted-average shares outstanding	161,777	165,713	161,716	174,023
Basic earnings per share (in dollars per share)	$ 0.35	$ 0.29	$ 1.17	$ 0.91
Diluted earnings per share (in dollars per share)	$ 0.35	$ 0.29	$ 1.16	$ 0.90
Anti-dilutive weighted-average shares from stock awards	1,572	2,807	2,416	3,287
Senior Notes Due 2019 [Member]
Denominator:
Convertible debt, conversion price (in dollars per share)	$ 90.00		$ 90.00