Treasury Stock	12 Months Ended
Dec. 31, 2018
Equity [Abstract]
Treasury Stock	(11) Treasury Stock The Board of Directors has authorized the Company’s repurchase of up to an aggregate of $800.0 million of its class A common stock from time to time on the open market through April 29, 2023 under the 2005 Share Repurchase Program, although the program may be suspended or discontinued by the Company at any time. The timing and amount of any shares repurchased will be determined by the Company’s management based on its evaluation of market conditions and other factors. The 2005 Share Repurchase Program may be funded using the Company’s working capital, as well as proceeds from any other funding arrangements that the Company may enter into in the future. During 2018, the Company repurchased an aggregate of 880,667 shares of its class A common stock at an average price per share of $126.02 and an aggregate cost of $111.0 million pursuant to the 2005 Share Repurchase Program. As of December 31, 2018, the Company had repurchased an aggregate of 4,707,614 shares of its class A common stock at an average price per share of $96.92 and an aggregate cost of $456.3 million pursuant to the 2005 Share Repurchase Program. The average price per share and aggregate cost amounts disclosed above include broker commissions. During the years ended December 31, 2017 and 2016, the Company did not repurchase any shares of its class A common stock pursuant to the 2005 Share Repurchase Program.

Treasury Stock

12 Months Ended

Dec. 31, 2018

(11) Treasury Stock

The Board of Directors has authorized the Company’s repurchase of up to an aggregate of $800.0 million of its class A common stock from time to time on the open market through April 29, 2023 under the 2005 Share Repurchase Program, although the program may be suspended or discontinued by the Company at any time. The timing and amount of any shares repurchased will be determined by the Company’s management based on its evaluation of market conditions and other factors. The 2005 Share Repurchase Program may be funded using the Company’s working capital, as well as proceeds from any other funding arrangements that the Company may enter into in the future. During 2018, the Company repurchased an aggregate of 880,667 shares of its class A common stock at an average price per share of $126.02 and an aggregate cost of $111.0 million pursuant to the 2005 Share Repurchase Program. As of December 31, 2018, the Company had repurchased an aggregate of 4,707,614 shares of its class A common stock at an average price per share of $96.92 and an aggregate cost of $456.3 million pursuant to the 2005 Share Repurchase Program. The average price per share and aggregate cost amounts disclosed above include broker commissions. During the years ended December 31, 2017 and 2016, the Company did not repurchase any shares of its class A common stock pursuant to the 2005 Share Repurchase Program.