On April 17, 2017, the Company’s Board of Directors adopted the 2017 Incentive Award Plan (the “2017 Plan”), which became effective upon approval by the Company’s stockholders on May 23, 2017.  The 2017 Plan replaced and superseded in its entirety the 2007 Incentive Award Plan (the “2007 Plan”), which expired pursuant to its terms on May 24, 2017.  A total of 10,000,000 shares of Class A Common Stock are reserved for issuance under the 2017 Plan, which provides for grants of ISOs, non-qualified stock options, restricted stock and various other types of equity awards as described in the plan to the employees, consultants and directors of the Company and its subsidiaries. The 2017 Plan is administered by the Company’s Board of Directors with respect to awards to non-employee directors and by the Company’s Compensation Committee with respect to other eligible participants.

For stock-based awards, the Company recognized compensation expense based on the grant date fair value. Share‑based compensation expense was $7.6 million and $7.5 million for the three months ended September 30, 2018 and 2017, respectively.  Share-based compensation expense was $23.6 million and $21.7 million for the nine months ended September 30, 2018 and 2017, respectively. During the three and nine months ended September 30, 2018, the Company redeemed 7,899 and 308,155 shares of Class A Common Stock for $0.2 million and $11.4 million to satisfy employee tax withholding requirements. No shares were redeemed during the three and nine months ended September 30, 2017.

A summary of the status and changes of the Company’s nonvested shares related to the 2007 Plan and the 2017 Plan, as of and for the nine months ended September 30, 2018 is presented below:

As of September 30, 2018, there was $82.4 million of unrecognized compensation cost related to nonvested common shares. The cost is expected to be amortized over a weighted average period of 2.8 years.

On April 17, 2017, the Company’s Board of Directors adopted the 2018 Employee Stock Purchase Plan (the “2018 ESPP”), which the Company’s stockholders approved on May 23, 2017. The 2018 Employee Stock Purchase Plan provides eligible employees of the Company and its subsidiaries with the opportunity to purchase shares of the Company’s Class A Common Stock at a purchase price equal to 85% of the Class A Common Stock’s fair market value on the first trading day or last trading day of each purchase period, whichever is lower. The 2018 ESPP generally provides for two six-month purchase periods every twelve months: June 1 through November 30 and December 1 through May 31, except that the initial purchase period under the 2018 ESPP had a duration of five months, commencing on January 1, 2018 and ending on May 31, 2018. Eligible employees participating in the 2018 ESPP will, for a purchase period, be able to invest up to 15% of their compensation through payroll deductions during each purchase period. A total of 5,000,000 shares of Class A Common Stock are available for issuance under the 2018 ESPP.