16.

Employee Retirement and Postretirement Benefits

Stock-Based Compensation — As of March 31, 2018, we had three stock-based employee compensation plans (“Stock Plans”). See Note 11, “Stock-Based Compensation,” in our 2017 10-K for further information regarding these plans. Most of our equity grants are awarded on an annual basis.

For the three month period ended March 31, 2018, options to purchase 2,239,417 shares of common stock (of which 633,012 are options that contain a market condition, in addition to the time-based vesting requirements) were granted, options to purchase 253,653 (of which 207,527 options contain a market condition) shares of common stock were forfeited, and options to purchase 288,250 shares of common stock expired.

For the three month period ended March 31, 2018, 696,260 Restricted Stock Units (“RSUs”) (of which 205,993 are RSUs that contain a market condition, in addition to the time-based vesting requirements) were granted, 148,302 RSUs vested and 58,045 RSUs (of which 33,692 contained a market condition) were forfeited.

For the three month period ended March 31, 2018, 14,271 shares vested. These shares are deemed issued as of the date of grant, but not outstanding until they vest.

For the three month period ended March 31, 2018, 25,331 Deferred Stock Units were granted and vested.

For the three month period ended March 31, 2018, 55,812 shares of common stock were issued under the employee stock purchase plan.

The following is a summary of our stock-based compensation expense by operating expense line in the unaudited condensed consolidated statements of operations (in thousands):


	For the Three Months
	Ended March 31,
	2018		2017
Cost of service revenue	$	434	$	458
Cost of equipment revenue		54		37
Engineering, design and development		910		850
Sales and marketing		1,082		749
General and administrative		1,906		2,236

Total stock-based compensation expense	$	4,386	$	4,330

401(k) Plan — Under our 401(k) plan, all employees who are eligible to participate, are entitled to make tax-deferred contributions, subject to Internal Revenue Service limitations. We match 100% of the employee’s first 4% of contributions made, subject to annual limitations. Our matching contributions were $1.2 million and $1.6 million, respectively, for the three month periods ended March 31, 2018 and 2017.