Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2020
Share-based Payment Arrangement [Abstract]  
Schedule of Stock-based Compensation Expense
The following table summarizes stock-based compensation expense recognized for the periods presented:
 
Three Months Ended June 30,
 
Six Months Ended June 30,
(in thousands)
2020
 
2019
 
2020
 
2019
Restricted stock awards
$
3,387

 
$
3,408

 
$
7,741

 
$
6,590

Stock option awards
291

 
2,625

 
1,275

 
5,209

Performance stock units
1,003

 
725

 
2,006

 
1,442

Other stock-based compensation expense(1)
46

 
—

 
114

 
—

Total stock-based compensation expense
$
4,727

 
$
6,758

 
$
11,136

 
$
13,241

 
(1)  
Includes expenses related to the Company’s Employee Stock Purchase Plan (the “ESPP”). In May 2019, an aggregate of 2,000,000 shares were authorized by stockholders for issuance under the ESPP, which became effective on July 1, 2019. As of June 30, 2020, the Company had 1,940,801 shares of Class A Common Stock available for future issuance.
Schedule of Restricted Stock Activity
The following table provides information about restricted stock activity during the six months ended June 30, 2020:
 
Awards
 
Weighted Average Grant-Date Fair Value
Unvested balance as of December 31, 2019
4,838,996

 
$
8.51

Granted
1,385,235

 
2.53

Vested
(540,402
)
 
8.52

Forfeited
(757,975
)
 
5.81

Unvested balance as of June 30, 2020
4,925,854

 
6.90
Summary of Stock Option Valuation Inputs
The following table summarizes the assumptions and related information used to determine the grant-date fair value of stock option awards for the periods presented:

Six Months Ended June 30,

2020

2019
Weighted average grant-date fair value per share
$
1.16


$
4.77

Expected term (in years)
6


6

Expected stock volatility
86
%

46
%
Dividend yield
—
%

—
%
Risk-free interest rate
1.0
%

2.4
%
Summary of Stock Option Activity
The following table provides information about stock option awards outstanding during the six months ended June 30, 2020:
 
Options
 
Weighted Average Exercise Price
 
Weighted Average Remaining Term
(in years)
 
Aggregate Intrinsic Value
(in thousands)
Outstanding as of December 31, 2019
4,764,167

 
$
15.99

 
 
 
 
Granted
124,000

 
2.13

 
 
 
 
Exercised
—

 
—

 
 
 

Forfeited
(94,409
)
 
13.99

 
 
 
 
Expired
(2,086,164
)
 
16.34

 
 
 
 
Outstanding as of June 30, 2020
2,707,594

 
15.15

 
6.4
 
$
40

Exercisable as of June 30, 2020
2,136,070

 
15.95

 
5.9
 
$
—