Rendering

Component: (Network and Table)
Network
2311301 - Disclosure - Stock-Based Compensation (Tables)
(http://www.acceleronpharma.com/role/StockBasedCompensationTables)
Table(Implied)
Slicers (applies to each fact value in each table cell)
Reporting Entity [Axis]0001280600 (http://www.sec.gov/CIK)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]Period [Axis]
2016-01-01 - 2016-12-31
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
 
Schedule of Total Compensation Cost Recognized for all Stock-based Awards
Total compensation cost recognized for all stock-based compensation awards in the consolidated statements of operations and comprehensive loss is as follows (in thousands):
 
Year Ended December 31,
 
2016
 
2015
 
2014
Research and development
$
8,171

 
$
4,852

 
$
2,065

General and administrative
10,386

 
7,223

 
2,713

 
$
18,557

 
$
12,075

 
$
4,778

  
Schedule of Stock Option Valuation Assumptions
The fair value of each option issued to employees was estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:
 
Year Ended December 31,
 
2016
 
2015
 
2014
Expected volatility
65.1
%
 
67.0
%
 
70.9
%
Expected term (in years)
6.0

 
6.0

 
6.0

Risk-free interest rate
1.69
%
 
1.67
%
 
1.82
%
Expected dividend yield
—
%
 
—
%
 
—
%
  
Summary of Stock Option Activity
The following table summarizes the stock option activity under the Company's stock option plans during the year ended December 31, 2016 (in thousands, except per share amounts and years):
 
Number
of Grants
 
Weighted-
Average
Exercise
Price Per
Share
 
Weighted-
Average
Contractual
Life
(in years)
 
Aggregate
Intrinsic
Value(1)
Outstanding at December 31, 2015
3,191

 
$
18.85

 
 
 
 
Granted
1,046

 
$
31.13

 
 
 
 

Exercised
(885
)
 
$
6.00

 
 
 
 

Canceled or forfeited
(36
)
 
$
36.45

 
 
 
 

Outstanding at December 31, 2016
3,316

 
$
25.96

 
7.03
 
$
18,562,282

Exercisable at December 31, 2016
1,779

 
$
19.36

 
5.43
 
$
18,421,393

Vested and expected to vest at December 31, 2016(2)
3,258

 
$
25.83

 
6.99
 
$
18,560,293

______________________________________________________
(1)
The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2016 and 2015.

(2)
This represents the number of vested options at December 31, 2016, plus the number of unvested options expected to vest at December 31, 2016, based on the unvested options outstanding at December 31, 2016, adjusted for the estimated forfeiture rate.
  
Schedule of Restricted Stock Unit Activity
The following table summarizes the restricted stock unit (RSU) activity under the 2013 Plan during the year ended December 31, 2016:
 
Number
of Grants
 
Weighted-
Average
Grant Date Fair Value
Unvested balance at December 31, 2015
521

 
$
31.57

Granted
221

 
$
31.56

Vested
—

 
$
—

Forfeited
(10
)
 
$
33.94

Unvested balance at December 31, 2016
732

 
$
31.55