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Debt (Tables)
 3 Months Ended
Mar. 31, 2019
Debt Disclosure [Abstract]  
Summary of convertible notes
The Convertible Notes consist of the following:
Liability component
 
March 31, 2019
 
December 31, 2018
Principal
 
$
150,000

 
$
150,000

Less: Debt issuance costs
 
(1,648
)
 
(1,746
)
Less: Debt discount, net(1)
 
(33,072
)
 
(35,054
)
Net carrying amount
 
$
115,280

 
$
113,200

 
(1) Included in the consolidated balance sheets within convertible senior notes (due 2022) and amortized to interest expense over the remaining life of the Convertible Notes using the effective interest rate method.
Summary of interest expense recognized related to the Convertible Notes
The following table sets forth total interest expense recognized related to the Convertible Notes:
 
 
Three Months Ended March 31,
 
 
2019
 
2018
Contractual interest expense
 
$
1,110

 
$
1,110

Amortization of debt issuance costs
 
99

 
89

Amortization of debt discount
 
1,982

 
1,780

Total
 
$
3,191

 
$
2,979

Effective interest rate of the liability component
 
11
%
 
11
%