12. Stock-Based Compensation Plans

The components of stock compensation expense for the three years ended December 31, 2018 were as follows:


	2018		2017		2016
	(in thousands)
2007 Stock Incentive Plan	$	5,353	$	4,207	$	3,681
Employee Stock Purchase Plan		57		63		36
Total Stock Compensation Expense	$	5,410	$	4,270	$	3,717

The significant stock compensation plans are described below.

The 2007 Stock Incentive Plan (the “2007 Plan”) was adopted on May 24, 2007. Under this 2007 Plan, a total of 2,800,000 shares are authorized for stock based compensation available in the form of either RSA’s or stock options. The RSA’s are subject to service-based vesting, typically between one and four years, where a specific period of continued employment must pass before an award vests. The expense associated with these awards is recognized on a straight-line basis over the respective vesting period, with forfeitures accounted for as they occur. For any vesting tranche of an award, the cumulative amount of compensation cost recognized is equal to the portion of the grant‑date fair value of the award tranche that is actually vested at that date. There are no stock options outstanding under the 2007 Plan.

The 2018 Stock Incentive Plan (the “2018 Plan”) was adopted on May 24, 2018. Under this 2018 Plan, a total of 800,000 shares are authorized for stock based compensation, plus the number of shares remaining under the 2007 Plan and any future forfeited awards under the 2007 and 2018 Plans, in the form of RSA’s. The RSA’s are subject to service-based vesting, typically between one and four years, where a specific period of continued employment must pass before an award vests. The expense associated with these awards is recognized on a straight-line basis over the respective vesting period, with forfeitures accounted for as they occur. For any vesting tranche of an award, the cumulative amount of compensation cost recognized is equal to the portion of the grant‑date fair value of the award tranche that is actually vested at that date.

As of December 31, 2018, the Company has granted 2,885,914 RSA’s under the 2007 Plan. Of this amount, 176,644 shares were cancelled and returned to the pool of shares which could be granted under the 2018 Plan resulting in a net number of 890,730 shares available for future issuance. The fair value of the RSA’s equaled the stock price at the grant date.

As of December 31, 2018, the Company has not granted RSA’s under the 2018 Plan.

The following table summarizes restricted stock activity under the 2007 Plan for the three years ended December 31, 2018:


		Weighted Average		Aggregate Grant
	Number Outstanding	Grant Date Fair Value		Date Fair Value
Balance as of December 31, 2015	396,595	$	17.98	$	7,131,200
Shares granted	136,645		21.55		2,944,941
Shares forfeited	(20,377)		17.79		(362,536)
Shares vested	(213,528)		17.12		(3,655,269)
Balance as of December 31, 2016	299,335		20.24		6,058,336
Shares granted	215,603		24.89		5,365,731
Shares forfeited	(10,999)		24.38		(268,200)
Shares vested	(175,817)		19.61		(3,448,628)
Balance as of December 31, 2017	328,122		23.49		7,707,239
Shares granted	270,454		33.91		9,172,223
Shares forfeited	(9,900)		32.06		(317,430)
Shares vested	(170,786)		22.25		(3,799,213)
Balance as of December 31, 2018	417,890	$	30.54	$	12,762,819

At December 31, 2018 the stock compensation expense related to the RSA’s that will be recognized over the average remaining vesting period of 1.8 years totaled $8.7 million. At December 31, 2018, the intrinsic value of unvested RSA’s was $14.5 million.

Under the Employee Stock Purchase Plan (“ESPP”), as amended and restated effective April 1, 2018, 325,000 shares of common stock have been reserved for issuance. Eligible employees may designate no more than 10% of their base cash compensation to be deducted each pay period for the purchase of common stock under the Purchase Plan. Participants may purchase no more than 1,000 shares or $25,000 of common stock in any one calendar year. Each January 31 and July 31 shares of common stock are purchased with the employees’ payroll deductions from the immediately preceding six months at a price per share of 85% of the lesser of the market price of the common stock on the purchase date or the market price of the common stock on the date of entry into an offering period. In 2018, 2017, and 2016, 11,132, 11,485, and 11,014 shares of common stock, respectively, were issued under the ESPP. The Company issues new shares through its transfer agent upon employee stock purchase. The weighted average per share fair value of the employee’s purchase rights under the Purchase Plan for the rights granted was $9.42, $7.39 and $6.35 for 2018, 2017 and 2016, respectively.