Quarterly report pursuant to Section 13 or 15(d)

Debt - Summary (Details)

v3.19.3
Debt - Summary (Details) - USD ($)
Sep. 30, 2019
Dec. 31, 2018
Dec. 31, 2014
Debt Instrument [Line Items]      
Revolving credit facility balance $ 100,000,000 $ 0  
Convertible Notes due 2019      
Debt Instrument [Line Items]      
Face amount 172,500,000 172,500,000 $ 172,500,000
Unaccreted discount on Convertible Notes (1,338,000) (5,890,000)  
Unamortized issuance costs on Convertible Notes (196,000) (899,000)  
Convertible Notes carrying value 170,966,000 165,711,000  
Convertible Notes due 2023      
Debt Instrument [Line Items]      
Face amount 345,000,000 345,000,000  
Unaccreted discount on Convertible Notes (35,805,000) (42,641,000)  
Unamortized issuance costs on Convertible Notes (6,410,000) (7,634,000)  
Convertible Notes carrying value $ 302,785,000 $ 294,725,000