Common Stock Repurchase Program	12 Months Ended
Dec. 31, 2018
Notes To Financial Statements [Abstract]
Share Repurchase Program Disclosure	Common Stock Repurchase Programs April 2014 Repurchase Program In April 2014, we announced that our Board of Directors had authorized a plan to repurchase up to $300.0 million of our common stock ("April 2014 Repurchase Program"). Prior to 2017, we entered into accelerated share purchase agreements to repurchase $190 million of our common stock and received a total of approximately 3.2 million shares. In addition, we repurchased on the open market approximately 1.6 million shares of our common stock for an aggregate purchase price of approximately $106.2 million. In 2017, we repurchased on the open market approximately 0.04 million shares of our common stock at an average price of $96.37 per share, including commission for an aggregate purchase price of approximately $3.8 million, completing the April 2014 Repurchase Program. April 2016 Repurchase Program In April 2016, we announced that our Board of Directors had authorized a plan to repurchase up to $300.0 million of our common stock ("April 2016 Repurchase Program"). In 2017, we entered into an accelerated share repurchase agreement ("2017 ASR") to repurchase $50.0 million of our common stock. The 2017 ASR was completed in August 2017. We received a total of approximately 0.4 million shares for an average share price of $146.48. During 2017, we repurchased on the open market approximately 0.2 million shares of our common stock at an average price of $243.40 per share, including commissions, for an aggregate purchase price of approximately $50.0 million. In 2018, we repurchased on the open market approximately 0.7 million shares of our common stock at an average price of $293.21 per share, including commission for an aggregate purchase price of approximately $200.0 million, completing the April 2016 Repurchase Program. May 2018 Repurchase Program In May 2018, we announced that our Board of Directors had authorized a plan to repurchase up to $600.0 million of our common stock ("May 2018 Repurchase Program"). In 2018, we repurchased on the open market approximately 0.1 million shares of our common stock at an average price of $356.54 per share, including commissions, for an aggregate purchase price of approximately $50.0 million. In November 2018, we entered into an accelerated stock repurchase agreement to repurchase $50.0 million of our common stock which was completed in December 2018. We received a total of approximately 0.2 million shares for an average share price of $213.18. As of December 31, 2018, we have $500.0 million remaining under the May 2018 Repurchase Program. In February 2019, we purchased on the open market approximately 0.2 million shares of our common stock at an average price of $243.42 per share, including commission for an aggregate purchase price of approximately of $50.0 million.

Common Stock Repurchase Programs

April 2014 Repurchase Program

In April 2014, we announced that our Board of Directors had authorized a plan to repurchase up to $300.0 million of our common stock ("April 2014 Repurchase Program").

Prior to 2017, we entered into accelerated share purchase agreements to repurchase $190 million of our common stock and received a total of approximately 3.2 million shares. In addition, we repurchased on the open market approximately 1.6 million shares of our common stock for an aggregate purchase price of approximately $106.2 million.

In 2017, we repurchased on the open market approximately 0.04 million shares of our common stock at an average price of $96.37 per share, including commission for an aggregate purchase price of approximately $3.8 million, completing the April 2014 Repurchase Program.

April 2016 Repurchase Program

In April 2016, we announced that our Board of Directors had authorized a plan to repurchase up to $300.0 million of our common stock ("April 2016 Repurchase Program").

In 2017, we entered into an accelerated share repurchase agreement ("2017 ASR") to repurchase $50.0 million of our common stock. The 2017 ASR was completed in August 2017. We received a total of approximately 0.4 million shares for an average share price of $146.48. During 2017, we repurchased on the open market approximately 0.2 million shares of our common stock at an average price of $243.40 per share, including commissions, for an aggregate purchase price of approximately $50.0 million.

In 2018, we repurchased on the open market approximately 0.7 million shares of our common stock at an average price of $293.21 per share, including commission for an aggregate purchase price of approximately $200.0 million, completing the April 2016 Repurchase Program.

May 2018 Repurchase Program

In May 2018, we announced that our Board of Directors had authorized a plan to repurchase up to $600.0 million of our common stock ("May 2018 Repurchase Program").

In 2018, we repurchased on the open market approximately 0.1 million shares of our common stock at an average price of $356.54 per share, including commissions, for an aggregate purchase price of approximately $50.0 million. In November 2018, we entered into an accelerated stock repurchase agreement to repurchase $50.0 million of our common stock which was completed in December 2018. We received a total of approximately 0.2 million shares for an average share price of $213.18. As of December 31, 2018, we have $500.0 million remaining under the May 2018 Repurchase Program.

In February 2019, we purchased on the open market approximately 0.2 million shares of our common stock at an average price of $243.42 per share, including commission for an aggregate purchase price of approximately of $50.0 million.