Note 15 - Restricted Stock Units

12 Months Ended

Dec. 31, 2020

Notes to Financial Statements

Share-based Payment Arrangement, Restricted Stock Units [Text Block]

15.         Restricted Stock Units

In 2019 and 2020, the Company issued Restricted Stock Units (“RSUs”) to certain employees which vest over three years. The RSUs vest on defined vesting dates, subject to the continuous service with the Company at the applicable vesting event. Vesting can be accelerated upon a change in control under the Plan if the RSUs are not assumed by the successor company, and will be accelerated for certain executive officers under existing employment agreements if any such executive officer has a termination of employment in connection with a change in control event.  When vested, the RSUs represent the right to be issued the number of shares of the Company’s common stock that is equal to the number of RSUs granted. The fair value of each RSU is estimated based upon the closing price of the Company’s common stock on the grant date. Share-based compensation expense related to RSUs is recognized over the requisite service period as adjusted for estimated forfeitures.

The following is a summary of the RSU activity for the years ended December 31, 2020 and 2019:

	Number of Restricted Stock Units Outstanding			Weighted Average Grant Date Fair Value
Unvested December 31, 2018		382,098		$	20.24
Granted		192,987			31.42
Vested		(85,153	)		25.98
Forfeited		(46,005	)		21.38
Unvested December 31, 2019		443,927		$	23.88
Granted		3,112,382			0.67
Vested		(354,808	)		19.38
Forfeited		(242,402	)		6.54
Unvested December 31, 2020		2,959,099		$	1.41

As of December 31, 2020 and 2019, the Company recorded approximately $1.7 million and $3.2 million, respectively, in compensation expense for the RSUs. As of December 31, 2020, the unrecognized stock-based compensation expense related to unvested RSUs was approximately $1.5 million, which is expected to be recognized over a weighted average period of approximately 1.1 years.