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Organization and Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2017
Accounting Policies [Abstract]  
Schedule of Assumptions Used to Estimate the Fair Value of Each Option Award

The fair value of each option award is estimated on the date of grant using the Black-Scholes-Merton valuation model using the assumptions noted in the following table.

 

 

 

Year Ended December 31,

 

 

 

2017

 

 

2016

 

 

2015

 

Assumptions:

 

 

 

 

 

 

 

 

 

 

 

 

Assumed risk-free interest rate

 

1.86%

 

 

1.44%

 

 

1.34%

 

Assumed volatility

 

72%

 

 

72%

 

 

68%

 

Average expected option life

 

4.5 years

 

 

4.5 years

 

 

4.5 years

 

Expected dividend yield

 

 

—

 

 

 

—

 

 

 

—