Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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

Debt - Convertible Debt (Details) - Convertible notes payable - USD ($) $ in Millions	Jun. 15, 2018	Dec. 31, 2017	Jun. 30, 2011
Debt Instrument [Line Items]
Principal amount		$ 316.3
Convertible Senior Notes Due June 2018
Debt Instrument [Line Items]
Principal amount			$ 316.3
Interest rate			2.75%
Extinguishment of debt	$ 316.3