Note 12. Stock Options

The following table summarizes the outstanding stock option activity during the periods indicated:

	Number of shares			Weighted average exercise price		Weighted average remaining contractual term
Balance at December 31, 2017		1,203,627		$	7.06		8.10
Granted		963,800			9.88		7.79
Exercised		(136,094	)		2.20		1.43
Expired/Forfeited		(75,458	)		10.43		0.04
Balance at June 30, 2018		1,955,875		$	8.66		6.73
Vested and exercisable at June 30, 2018		867,417		$	7.07		3.76
Vested and expected to vest at June 30, 2018		1,955,875		$	8.66		6.73

The weighted average grant date fair value of options granted during the six months ended June 30, 2018 and for the year ended December 31, 2017 was $3.98 and $6.02, respectively. For fully vested stock options, the aggregate intrinsic value as of June 30, 2018 and December 31, 2017 was $3,358,788 and $3,596,624, respectively. For stock options expected to vest, the aggregate intrinsic value as of June 30, 2018 and December 31, 2017 was $1,065,896 and $1,469,154, respectively.

At June 30, 2018 and December 31, 2017, there was $3,777,271 and $2,453,342, respectively, of total unrecognized compensation cost related to unvested stock options granted under the Company’s equity plans. That cost is expected to be recognized over the next three years and is based on the date the options were granted.

The Company currently uses authorized and unissued shares to satisfy share award exercises.