Stock-Based Compensation (Tables)
 3 Months Ended
Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Components of the Company’s stock-based compensation expense
The following table summarizes the components of the Company’s stock-based compensation expense included in general and administrative expenses in the Consolidated Statements of Comprehensive Income for the three months ended March 31, 2015 and 2014:
 
 
Three Months Ended
 
 
March 31,
 
 
2015
 
2014
 
(In millions)
Total stock-based compensation expense:
 
 
 
 
Equity classified awards expense
 
$
2.4

 
$
3.2

Liability classified awards expense (credit)
 
0.3

 
(0.2
)
Total pre-tax stock-based compensation expense
 
2.7

 
3.0

Tax benefit
 
(1.0
)
 
(1.1
)
Total stock-based compensation expense, net of tax
 
$
1.7

 
$
1.9
Schedule of stock option valuation assumptions
The following summarizes the assumptions used in the Black-Scholes model:
 
Risk-free interest rate
1.56
%
Weighted average historical volatility
37.5
%
Dividend yield
3.10
%
Expected years until exercise
4.50

Forfeitures
11.0
%
Weighted average fair value of options granted
$28.37
Schedule of stock option activity

Stock option balances as of March 31, 2015 and activity related to stock options for the three months ended March 31, 2015 were as follows:
 
 
Shares
 
Weighted
Average
Exercise
Price
 
Weighted Average
Remaining
Contractual Term
(in Years)
 
Aggregate
Intrinsic
Value (in Millions)
Outstanding at December 31, 2014
 
618,115

 
$
53.10

 
 
 
 
Granted
 
117,511

 
113.72

 
 
 
 
Exercised
 
(194,648
)
 
42.16

 
 
 
 
Outstanding at March 31, 2015
 
540,978

 
70.21

 
7.5
 
$20.7
Vested at March 31, 2015 and Expected to Vest
 
499,627

 
67.67

 
7.4
 
$20.3
Exercisable at March 31, 2015
 
327,100

 
$
51.83

 
6.4
 
$18.0
Schedule of restricted stock unit activity
Outstanding balances as of March 31, 2015 and activity related to restricted stock and restricted stock units for the three months ended March 31, 2015 were as follows:
 
 
Restricted
Stock
 
Weighted
Average
Grant Date
Fair Value
 
Restricted
Stock Units
 
Weighted
Average
Grant Date
Fair Value
Outstanding at December 31, 2014
 
233,818

 
$
70.14

 
41,622

 
$
66.92

Granted
 
63,728

 
113.62

 
9,695

 
113.72

Released
 
(61,974
)
 
52.30

 
(13,567
)
 
52.19

Forfeited
 
(5,413
)
 
72.97

 
—

 
—

Outstanding at March 31, 2015
 
230,159

 
$
86.91

 
37,750

 
$
86.54