Capital Stock (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) Vote $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares	Oct. 31, 2015 USD ($)	Aug. 31, 2013 USD ($)	Dec. 31, 1998 USD ($)
Capital stock [Abstract]
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001
Weighted average share outstanding [Abstract]
Basic weighted-average common shares outstanding (in shares)	57,997,000	59,073,000	58,606,000
Effect of dilutive securities: Stock awards and options (in shares)	1,060,000	1,814,000	2,842,000
Diluted weighted-average common shares outstanding (in shares)	59,057,000	60,887,000	61,448,000
Anti-dilutive securities excluded from calculation of diluted earnings per share (in shares)	1,800,000	2,700,000	1,200,000
Repurchases of common stock [Abstract]
Common stock repurchased | $	$ 164,094	$ 45,724	$ 140,865
Amount available for repurchases | $	$ 446,900
Preferred Stock [Member]
Capital stock [Abstract]
Preferred stock, authorized (in shares)	25,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001
Shares outstanding (in shares)	0	0
Common Class A [Member]
Capital stock [Abstract]
Common stock, authorized (in shares)	500,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Number of votes per share | Vote	1
Number of shares of class A common stock issued after conversion of Class B common stock		1
Repurchases of common stock [Abstract]
Shares repurchased (in shares)	3,800,000	800,000	1,700,000
Common stock repurchased | $	$ 164,100	$ 45,724	$ 140,865
Authorized amount | $				$ 10,000		$ 500,000
Increase in authorized amount | $					$ 400,000
Common Class B [Member]
Capital stock [Abstract]
Common stock, authorized (in shares)	100,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Shares outstanding (in shares)	0	0
Number of votes per share | Vote	10