Common Stock Repurchase	9 Months Ended
Sep. 30, 2017
Notes To Financial Statements [Abstract]
Common Stock Repurchase	Common Stock Repurchase April 2014 Repurchase Program In April 2014, we announced that our Board of Directors had authorized a stock repurchase program ("April 2014 Repurchase Plan") pursuant to which we may purchase up to $300.0 million of our common stock over the next three years. During the first quarter of 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. All repurchased shares were retired. April 2016 Repurchase Program In April 2016, we announced that our Board of Directors had authorized an additional plan to repurchase up to $300.0 million of the Company's stock ("April 2016 Repurchase Program"). On May 2, 2017, we entered into an accelerated share repurchase ("ASR") to repurchase $50.0 million of our common stock ("2017 ASR"). The 2017 ASR was completed on August 3, 2017. The final number of shares repurchased was based on our volume-weighted average stock price during the term of the transaction, less an agreed upon discount. We received a total of approximately 0.4 million shares at a weighted average share price of $146.48 under the 2017 ASR. All repurchased shares were retired. As of September 30, 2017, we have $250.0 million remaining under the April 2016 Repurchase Plan.

Common Stock Repurchase

April 2014 Repurchase Program

In April 2014, we announced that our Board of Directors had authorized a stock repurchase program ("April 2014 Repurchase Plan") pursuant to which we may purchase up to $300.0 million of our common stock over the next three years.

During the first quarter of 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. All repurchased shares were retired.

April 2016 Repurchase Program

In April 2016, we announced that our Board of Directors had authorized an additional plan to repurchase up to $300.0 million of the Company's stock ("April 2016 Repurchase Program").

On May 2, 2017, we entered into an accelerated share repurchase ("ASR") to repurchase $50.0 million of our common stock ("2017 ASR"). The 2017 ASR was completed on August 3, 2017. The final number of shares repurchased was based on our volume-weighted average stock price during the term of the transaction, less an agreed upon discount. We received a total of approximately 0.4 million shares at a weighted average share price of $146.48 under the 2017 ASR. All repurchased shares were retired. As of September 30, 2017, we have $250.0 million remaining under the April 2016 Repurchase Plan.