Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value
The following are the weighted-average assumptions used for grants issued:
 
For the years ended
 
December 31,
2015
 
December 31,
2014
 
December 31,
2013
 
 
 
 
 
 
Volatility
23.85
%
 
32.84
%
 
30.88
%
Risk-free interest rate
1.88
%
 
2.16
%
 
1.52
%
Expected term (years)
6.5

 
6.5

 
6.5

Dividend yield
—

 
—

 
—

Grant-date fair value
$
5.74

 
$
5.15

 
$
2.14
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value
The following table summarizes stock option activity during the year and also presents stock options outstanding and exercisable as of December 31, 2015 (dollars in millions, except for per share data):




Number of
Shares
 
Weighted Average Exercise Price Per Share
 
Weighted Average Remaining Contractual Life (In Years)
 
Aggregate Intrinsic Value
 
 
 
 
 
 
 
 
Outstanding, December 31, 2014
4,671,639

 
$
5.88

 

 
 
Granted
110,825

 
$
20.00

 

 
 
Exercised
(396,010
)
 
$
5.68

 

 
 
Forfeited
(14,700
)
 
$
13.47

 

 
 
Expired
(5,457
)
 
$
6.12

 

 
 
Outstanding, December 31, 2015
4,366,297

 
$
6.24

 
7.09
 
$
54.7

Exercisable, December 31, 2015
2,225,613

 
$
5.72

 
6.99
 
$
29.0
Schedule of Unrecognized Compensation Cost, Nonvested Awards
Unrecognized stock-based compensation expense related to outstanding unvested stock options is expected to be recognized in the Company’s statements of income as follows (by fiscal year):

(dollars in thousands)
 
2016
$
1,857

2017
1,709

2018
309

2019
121

2020
51

Total
$
4,047