June 30,

December 31,

2018

2017

Convertible Notes due 2019

$

172,500

$

172,500

Unaccreted discount on Convertible Notes due 2019

(8,832)

(11,677)

Unamortized issuance costs on Convertible Notes due 2019

(1,369)

(1,833)

Convertible Notes due 2019 carrying value

$

162,299

$

158,990

Convertible Notes due 2023

$

345,000

$

 —

Unaccreted discount on Convertible Notes due 2023

(47,016)

 —

Unamortized issuance costs on Convertible Notes due 2023

(8,422)

 —

Convertible Notes due 2023 carrying value

$

289,562

$

 —

Revolving credit facility balance

$

 —

$

81,168