Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Stock-based Compensation Expense
The following table summarizes stock-based compensation expense recognized for the periods presented:
 
For the Three Months Ended March 31,
(in thousands)
2019
 
2018
Restricted stock awards
$
3,182

 
$
1,775

Stock option awards
2,584

 
2,206

Performance stock units
717

 
352

Total stock-based compensation expense
$
6,483

 
$
4,333
Schedule of Restricted Stock Activity
The following table provides information about restricted stock activity during the three months ended March 31, 2019:
 
Awards
 
Weighted Average Grant Date Fair Value
Unvested balance as of December 31, 2018
1,535,945

 
$
17.88

Granted
436,210

 
12.51

Vested
(117,731
)
 
18.71

Forfeited
—

 
—

Unvested balance as of March 31, 2019
1,854,424

 
16.57
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 options awarded during the three months ended March 31, 2019 and 2018:

For the Three Months Ended March 31,

2019

2018
Weighted average grant-date fair value per share
$
5.22


$
7.96

Expected term (in years)
6


6

Expected stock volatility
45
%

37
%
Dividend yield
—
%

—
%
Risk-free interest rate
2.5
%

2.3
%
Summary of Stock Option Activity
The following table provides information about stock option awards outstanding during the three months ended March 31, 2019:
 
Options
 
Weighted Average Exercise Price
 
Weighted Average Remaining Term
(in years)
 
Aggregate Intrinsic Value
(in thousands)
Outstanding as of December 31, 2018
4,559,334

 
$
16.55

 
 
 
 
Granted
137,500

 
11.30

 
 
 
 
Exercised
—

 
—

 
 
 

Forfeited
(2,667
)
 
18.03

 
 
 
 
Expired
(333
)
 
18.48

 
 
 
 
Outstanding as of March 31, 2019
4,693,834

 
16.40

 
8.0
 
$
—

Exercisable as of March 31, 2019
2,531,133

 
16.09

 
7.7
 
$
—