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Share-Based Compensation | 6 Months Ended
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Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Share-Based Compensation | SHARE-BASED COMPENSATION The fair value of options, restricted stock units, deferred stock units and employee stock purchase rights awarded during the three and six months ended June 30, 2018, totaled $1.7 million and $32.8 million, respectively, as compared to $1.6 million and $29.5 million for the three and six months ended June 30, 2017, respectively. The total unrecognized compensation expense, net of estimated forfeitures, for unvested share-based compensation awards outstanding at June 30, 2018, was $62.8 million, which will be recognized over a weighted average period of approximately 2.1 years. During the three and six months ended June 30, 2018, we recognized expense of $6.5 million and $12.4 million, respectively, as compared to $6.0 million and $11.7 million for the three and six months ended June 30, 2017, respectively, related to share-based compensation. We determine the assumptions used in the valuation of option awards as of the date of grant. Differences in the expected stock price volatility, expected term or risk-free interest rate may necessitate distinct valuation assumptions at each grant date. As such, we may use different assumptions for options granted throughout the year. Option awards are granted with an exercise price equal to the closing market price of our common stock at the date of grant. We have never paid any cash dividends on our common stock, and we have no intention to pay such a dividend at this time; therefore, we assume that no dividends will be paid over the expected terms of option awards. The weighted averages of the valuation assumptions used to determine the fair value of each option award on the date of grant and the weighted average estimated fair values were as follows:
﻿ | For the Six Months Ended June 30,
﻿ | 2018 |  | 2017
﻿ |  |  |  |  |
Share price at grant | $ | 179.56 |  |  | $ | 142.66 |
Expected stock price volatility | 24 | % |  | 26 | %
Expected term, in years | 5.8 |  |  | 5.8 |
Risk-free interest rate | 2.7 | % |  | 2.0 | %
Weighted average fair value of options granted | $ | 52.99 |  |  | $ | 40.79 |

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- Definition The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -URI http://asc.fasb.org/topic&trid=2228938 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -URI http://asc.fasb.org/subtopic&trid=2208855 + Details
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