XML 79 R66.htm IDEA: XBRL DOCUMENT v3.10.0.1
Debt - Summary of convertible notes (Details) - Convertible debt - 3.00% Convertible senior notes due 2022 - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Aug. 31, 2015
Long-term debt      
Principal $ 150,000,000 $ 150,000,000 $ 150,000,000
Less: Debt issuance costs (1,746,000) (2,121,000)  
Less: Debt discount, net (35,054,000) (42,572,000)  
Net carrying amount $ 113,200,000 $ 105,307,000