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		638,300			10.75		9.81
Exercised		(52,970	)		1.96		3.92
Expired/Forfeited		(53,499	)		9.55		0.06
Balance at March 31, 2018		1,735,458		$	8.49		8.57
Vested and exercisable at March 31, 2018		499,046		$	2.25		6.72
Vested and expected to vest at March 31, 2018		1,735,458		$	8.49		8.57

The weighted average grant date fair value of options granted during the three months ended March 31, 2018 and for the year ended December 31, 2017 was $4.31 and $6.02, respectively. For fully vested stock options, the aggregate intrinsic value as of March 31, 2018 and December 31, 2017 was $2,804,129 and $3,596,624, respectively. For stock options expected to vest, the aggregate intrinsic value as of March 31, 2018 and December 31, 2017 was $921,408 and $1,469,154, respectively.

At March 31, 2018 and December 31, 2017, there was $4,594,157 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.