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Convertible Senior Notes
 12 Months Ended
Dec. 31, 2019
Debt Disclosure [Abstract]  
Convertible Senior Notes CONVERTIBLE SENIOR NOTES
Overview of 2013 Convertible Notes
On December 17, 2013, we entered into an agreement for the sale of $120 million aggregate principal amount of 2.75% Convertible Senior Notes (the “2013 Convertible Notes”). During 2016 and 2017, we completed certain open market purchases to retire $79.5 million of note principal.
The 2013 Convertible Notes matured on December 15, 2018. Substantially all then-outstanding notes were converted into our common stock at a rate of 95 shares per $1,000 principal units.
Components of Interest Expense on 2013 Convertible Notes
The following table sets forth the components of interest expense recognized in the accompanying Consolidated Statements of Operations for the 2013 Convertible Notes:
 
 
December 31,
 
 
2018
 
2017
Stated coupon interest expense
 
$
981

 
$
2,615

Amortization of debt issuance costs
 
220

 
567

Accretion of debt discount
 
1,931

 
4,890

Total interest expense
 
$
3,132

 
$
8,072

Effective interest rate
 
8.41
%
 
8.41
%