Convertible Senior Notes - Fair Value and Carrying Value of Convertible Senior Notes (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Convertible senior notes, Fair Value
Debt Instrument [Line Items]
Convertible senior notes, Fair Value	$ 161,717
Convertible senior notes, Carrying Value
Debt Instrument [Line Items]
Convertible senior notes, Fair Value	$ 109,772

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

No definition available.

Name:	us-gaap_ConvertibleDebtFairValueDisclosures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant