Capital Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Weighted average share outstanding [Abstract]
Basic weighted-average common shares outstanding (in shares)	59,073,000	58,606,000	60,600,000
Effect of dilutive securities: Stock awards and options (in shares)	1,814,000	2,842,000	2,425,000
Diluted weighted-average common shares outstanding (in shares)	60,887,000	61,448,000	63,025,000
Securities excluded from the calculation of diluted earnings per share	2,700,000	1,200,000	100,000
Common stock repurchased	$ 45,724,000	$ 140,865,000	$ 201,471,000
Increment authorized by the Company's board of directors under the stock repurchase program	400,000,000		250,000,000
Amount available for repurchases	348,800,000
Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, authorized (in shares)	25,000,000
Preferred stock, par value (in dollars per share)	$ 0.001
Shares outstanding (in shares)	0	0
Common Class A [Member]
Class of Stock [Line Items]
Common stock, authorized (in shares)	500,000,000
Common stock, par value (in dollars per share)	$ 0.001
Number of votes class is entitled to	1
Number of shares of class A common stock issued after conversion of Class B common stock		1
Weighted average share outstanding [Abstract]
Shares repurchased (in shares)	800,000	1,700,000	4,600,000
Common stock repurchased	$ 45,724,000	$ 140,865,000	$ 201,471,000
Common Class B [Member]
Class of Stock [Line Items]
Common stock, authorized (in shares)	100,000,000
Common stock, par value (in dollars per share)	$ 0.001
Shares outstanding (in shares)	0
Number of votes class is entitled to	10