6. Stock-Based Compensation

We have a long-term incentive plan (“LTIP”) to incentivize individuals providing services to us or our affiliates. The LTIP provides for the grant, from time to time, at the discretion of our compensation committee of our board of directors, of stock options, stock appreciation rights, restricted stock, restricted stock units, stock awards, dividend equivalents, other stock-based awards, cash awards, substitute awards and performance awards. Any individual who is an officer or employee or an officer or employee of any of our affiliates, and any other person who provides services to us or our affiliates, including members of our board of directors, will be eligible to receive awards under the LTIP at the discretion of our board of directors. As of December 31, 2019, 2.0 million stock awards were available for grant.

Restricted Stock Units

Restricted stock units (“RSUs”) granted pursuant to the LTIP are expected to be settled in shares of our Class A common stock if they vest. RSU’s generally vest over a three-year period; however, RSUs granted to our non-employee directors generally vest on the first anniversary of the grant.

A summary of restricted stock unit awards for the year ended December 31, 2019 is as follows (units in thousands):



	No. of RSUs		Weighted Average Grant Date Fair Value
Nonvested as of December 31, 2018		782	$	19.84
Granted		221	$	37.04
Vested		(274)	$	19.50
Forfeited		(39)	$	22.48
Nonvested as of December 31, 2019		690	$	25.34

During the year ended December 31, 2019 and 2018, we recorded $7.0 million and $4.7 million, respectively, of stock-based compensation expense. We did not recognize any stock-based compensation expense during 2017. Stock-based compensation expense is primarily recorded in selling, general and administrative expenses. There was approximately $11.1 million of unrecognized compensation expense relating to the unvested RSUs as of December 31, 2019. The unrecognized compensation expense will be recognized over the weighted average remaining vesting period of 2.0 years.