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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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

Guarantor and Non-Guarantor Financial Information - Debt (Details) - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2015	Dec. 31, 2017	Mar. 19, 2015
Financial Information
Percentage ownership of subsidiary	100.00%
Unsecured senior notes issued March 19, 2015
Financial Information
Debt issued		$ 500.0	$ 500.0
Issuer Subsidiary \| Unsecured senior notes issued March 19, 2015
Financial Information
Debt issued	$ 500.0