9.  STOCK-BASED COMPENSATION

The Company’s 2011 Equity Incentive Plan (“2011 Plan”) provides for the grant of up to an aggregate of 1,000,000 shares of restricted stock, restricted share units, stock appreciation rights, dividend or dividend equivalent rights, stock awards and other awards valued in whole or in part by reference to or otherwise based on the Company’s common stock, to officers, employees and directors of the Company. The 2011 Plan was approved by the Company’s shareholders at the 2012 Annual Meeting. At March 31, 2018, 361,438 shares remained available to be issued under the 2011 Plan. Compensation cost is measured at the date of the grant and is recognized in earnings over the period in which the shares vest. Restricted stock expense for the three months ended March 31, 2018, and April 1, 2017, totaled $495 and $697, respectively.

The following table summarizes restricted stock activity from December 30, 2017 through March 31, 2018:

The Company had $6,908 of total unrecognized compensation cost related to restricted stock awards granted under the 2011 Plan as of March 31, 2018. That cost is expected to be recognized over a weighted average period of 2.24 years.

The Company maintains an Employee Stock Purchase Plan (“ESPP”) in which only Sun Hydraulics US employees are eligible to participate. Employees in the United States who choose to participate are granted an opportunity to purchase common stock at 85 percent of market value on the first or last day of the quarterly purchase period, whichever is lower. Employees in the United Kingdom, under a separate plan, are granted an opportunity to purchase the Company’s common stock at market value, on the first or last day of the quarterly purchase period, whichever is lower, with the Company issuing one additional free share of common stock for each six shares purchased by the employee under the plan. The ESPP and U.K. plans authorize the issuance, and the purchase by employees, of up to 1,096,875 shares of common stock through payroll deductions. No U.S. employee is allowed to buy more than $25 of common stock in any year, based on the market value of the common stock at the beginning of the purchase period, and no U.K. employee is allowed to buy more than the lesser of £1.5 or 10% of his or her annual salary in any year. Employees purchased 8,110 shares at a weighted average price of $45.79, and 6,627 shares at a weighted average price of $30.96, under the ESPP and U.K. plans during the three months ended March 31, 2018, and April 1, 2017, respectively. The Company recognized $63 and $34 of compensation expense during the three months ended March 31, 2018, and April 1, 2017, respectively. At March 31, 2018, 538,199 shares remained available to be issued through the ESPP and the U.K. plan.

In March 2012, the Board of Directors adopted the Sun Hydraulics Corporation 2012 Nonemployee Director Fees Plan (the “2012 Directors Plan”), which was approved by the shareholders of the Company at the 2012 Annual Meeting. Under the 2012 Directors Plan, Nonemployee Directors are compensated for their Board service solely in shares of common stock.  In February 2015, the Board adopted amendments to the 2012 Directors Plan, which revised the compensation for Nonemployee Directors. Each Nonemployee Director now receives an annual retainer of 2,000 shares of common stock. The Chairman’s retainer is twice that of a regular director, and the retainer for the chairs of each Board Committee is 150% that of a regular director.  In addition, each Nonemployee Director receives 250 shares of common stock for attendance at each Board meeting and each meeting of each committee of the Board on which he or she serves when the committee meeting is not held within one day of a meeting of the Board. In June 2015, the Company's shareholders approved the amendments to the 2012 Directors Plan.

The Board has the authority to change from time to time, in any manner it deems desirable or appropriate, the share compensation to be awarded to all or any one or more Nonemployee Directors under the 2012 Directors Plan, provided that, with limited exceptions, such changes are subject to prior shareholder approval. The aggregate number of shares which may be issued during any single calendar year is limited to 35,000 shares. The 2012 Directors Plan authorizes the issuance of up to 270,000 shares of common stock. At March 31, 2018, 142,249 shares remained available for issuance under the 2012 Directors Plan. Directors were granted 6,625 and 6,375 shares for the three months ended March 31, 2018 and April 1, 2017, respectively. The Company recognized director stock compensation expense of $365 and $226 for the three months ended March 31, 2018 and April 1, 2017, respectively.