Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Stock Option Activity
A summary of our stock option activity for the three months ended March 31, 2018, is as follows (number of shares in thousands):
 
 
Number of
Shares
 
Weighted
Average
Exercise
Price per Share
 
Weighted
Average
Remaining
Contractual Life
in Years
Options outstanding as of December 31, 2017
 
1,692

 
$
10.81

 
7.3
Options granted
 
—

 
—

 
 
Options exercised
 
(98
)
 
4.81

 
 
Options cancelled/forfeited
 
(1
)
 
14.35

 
 
Options outstanding as of March 31, 2018
 
1,593

 
$
11.18

 
7.5
Schedule of Valuation Assumptions, Stock Options
The following table summarizes information relating to our stock options granted during the three months ended March 31, 2017: 
 
 
Three Months Ended
March 31, 2017
Stock options granted (in thousands)
 
132

Weighted average exercise price per share
 
$
23.80

Weighted average grant-date fair value per share
 
$
9.29

Weighted average Black-Scholes model assumptions:
 
 
Risk-free interest rate
 
2.04
%
Expected term (in years)
 
6.4

Expected volatility
 
35
%
Expected dividend yield
 
—
Schedule of Restricted Stock Units Activity
A summary of activity in connection with our RSUs for the three months ended March 31, 2018 is as follows (number of shares in thousands):
 
 
Number of Shares
 
Weighted- Average Grant Date Fair Value per Share
Unvested as of December 31, 2017
 
598

 
$
19.75

Granted
 
191

 
40.24

Vested
 
(107
)
 
13.36

Forfeited
 
(4
)
 
30.43

Unvested as of March 31, 2018
 
678

 
$
26.49
Schedule of Restricted Stock Awards Activity
A summary of activity in connection with our restricted stock awards for the three months ended March 31, 2018, is as follows (number of shares in thousands): 
 
 
Number of
Shares
 
Weighted-Average
Grant Date
Fair Value per Share
Unvested as of December 31, 2017
 
16

 
$
20.93

Granted
 
—

 
—

Vested
 
(2
)
 
5.64

Forfeited
 
—

 
—

Unvested as of March 31, 2018
 
14

 
$
22.55