XML 61 R50.htm IDEA: XBRL DOCUMENT v3.10.0.1
Debt - Convertible Notes (Details) - 3.00% Convertible senior notes due 2022 - Convertible debt - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Aug. 31, 2015
Long-term debt      
Principal $ 150,000,000 $ 150,000,000 $ 150,000,000.0
Less: Debt issuance costs (1,939,000) (2,121,000)  
Less: Debt discount, net (38,929,000) (42,572,000)  
Net carrying amount $ 109,132,000 $ 105,307,000