Common Stock Repurchase Programs	9 Months Ended
Sep. 30, 2017
Equity [Abstract]
Common Stock Repurchase Programs	13. Common Stock Repurchase Programs On November 9, 2015, the board of directors approved the repurchase of $150 million of outstanding common stock commencing January 1, 2016. On September 11, 2017, the board of directors approved the repurchase of an additional $125 million for our share repurchase program commencing September 11, 2017. At that time, $28.8 million remained available for repurchase under the 2015 authorization. The 2017 authorization thereby increased the repurchase authorization to $153.8 million of our common stock. This authorization expires December 31, 2018. Under this publicly announced plan, we repurchased 0.3 and 1.0 million shares for an aggregate purchase price of $12.5 and $47.0 million during the three and nine months ended September 30, 2017, respectively. We repurchased 0.4 and 1.4 million shares for an aggregate purchase price of $18.0 and $57.7 million during the nine months ended September 30, 2016, respectively. Our employees have the option to surrender shares of common stock to satisfy their tax withholding obligations that arise on the vesting of RSUs. In connection with stock option exercises, certain employees can surrender shares to satisfy the exercise price of certain stock options and any tax withholding obligations incurred in connection with such exercises. Employees surrendered less than 0.1 and 0.2 million shares for an aggregate purchase price of $3.1 and $10.0 million during the three and nine months ended September 30, 2017, respectively, and less than 0.1 and 0.2 million shares for an aggregate purchase price of $3.4 and $7.6 million during the three and nine months ended September 30, 2016, respectively. These repurchased shares reduce shares outstanding and are recorded as treasury stock under the cost method thereby reducing stockholders’ equity by the cost of the repurchased shares. Our repurchase program is limited by SEC regulations and is subject to compliance with our insider trading policy.

13. Common Stock Repurchase Programs

On November 9, 2015, the board of directors approved the repurchase of $150 million of outstanding common stock commencing January 1, 2016. On September 11, 2017, the board of directors approved the repurchase of an additional $125 million for our share repurchase program commencing September 11, 2017. At that time, $28.8 million remained available for repurchase under the 2015 authorization. The 2017 authorization thereby increased the repurchase authorization to $153.8 million of our common stock. This authorization expires December 31, 2018. Under this publicly announced plan, we repurchased 0.3 and 1.0 million shares for an aggregate purchase price of $12.5 and $47.0 million during the three and nine months ended September 30, 2017, respectively. We repurchased 0.4 and 1.4 million shares for an aggregate purchase price of $18.0 and $57.7 million during the nine months ended September 30, 2016, respectively.

Our employees have the option to surrender shares of common stock to satisfy their tax withholding obligations that arise on the vesting of RSUs. In connection with stock option exercises, certain employees can surrender shares to satisfy the exercise price of certain stock options and any tax withholding obligations incurred in connection with such exercises. Employees surrendered less than 0.1 and 0.2 million shares for an aggregate purchase price of $3.1 and $10.0 million during the three and nine months ended September 30, 2017, respectively, and less than 0.1 and 0.2 million shares for an aggregate purchase price of $3.4 and $7.6 million during the three and nine months ended September 30, 2016, respectively.

These repurchased shares reduce shares outstanding and are recorded as treasury stock under the cost method thereby reducing stockholders’ equity by the cost of the repurchased shares. Our repurchase program is limited by SEC regulations and is subject to compliance with our insider trading policy.