Stock-Based Compensation
 3 Months Ended
Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-Based Compensation
Stock-Based Compensation

During the three months ended March 31, 2015 and 2014, the Company recorded stock-based compensation expense of $8.8 million and $6.8 million, respectively. There were 3,130,460 and 272,082 stock-based awards available for grant under the Long-Term Incentive Plan ("LTIP") and the plans assumed in connection with the merger with Catalyst Health Solutions, Inc. ("Assumed Plans"), respectively, as of March 31, 2015.
(i) Stock options

The Black-Scholes option-pricing model was used to estimate the fair value of the stock options issued in each period at the grant date. Below is a summary of options granted and the assumptions utilized to derive fair value of the stock options under the Black-Scholes option-pricing model:
 
Three Months Ended March 31,
 
2015
 
2014
Total stock options granted
362,718

 
412,724

Volatility
36.3
%
 
38.7-39.2%

Risk-free interest rate
1.6
%
 
1.54-1.73%

Expected life (in years)
4.5

 
4.5

Dividend yield
—

 
—

Weighted-average grant date fair value
$ 16.16

 
$
15.51



The table below summarizes the stock options outstanding as of March 31, 2015 under both plans.
 
 
Options Outstanding
 
Weighted Average Exercise Price
 
Unrecognized Compensation Cost
 
Weighted Average Period
 
 
 
 
 
 
(in thousands)
 
 
LTIP
 
1,607,935

 
$
38.73

 
$
11,555

 
2.89
Assumed Plans
 
198,491

 
$
47.54

 
$
2,389

 
3.25


(ii) Restricted stock units

During the three months ended March 31, 2015, the Company granted time-based RSUs and performance-based RSUs to its employees and non-employee directors under both the LTIP and the Assumed Plans. Time-based RSUs either vest on a straight-line basis over a range of two to four years, or cliff vest after a three to four year period. Performance-based RSUs cliff vest based upon reaching agreed upon three-year performance conditions. The number of outstanding performance-based RSUs as of March 31, 2015 stated below assumes the associated performance targets will be met at the maximum level.

The table below summarizes the number of time-based and performance-based RSUs that were granted and outstanding under both plans for the three months ended March 31, 2015:
 
LTIP Plan
 
Assumed Plans
 
Number of Restricted Stock Units
 
Number of Restricted Stock Units
 
Time-Based
 
Performance - Based
 
Weighted Average Grant Date Fair Value Per Unit
 
Time-Based
 
Performance - Based
 
Weighted Average Grant Date Fair Value Per Unit
Granted
297,764

 
478,652

 
$
49.65

 
186,218

 
101,672

 
$
49.65

Outstanding
741,044

 
1,104,620

 
$
48.34

 
373,212

 
188,620

 
$
48.04






The table below summarizes the unrecognized compensation cost related to the outstanding RSUs at March 31, 2015.
 
Unrecognized Compensation Cost
 
Weighted Average Period
 
(in thousands)
 
 
LTIP
$
64,874

 
2.55
Assumed Plans
$
23,116

 
2.98