Preferred Stock Purchase Rights - Narrative (Details)	Dec. 31, 2017 shares
Equity [Abstract]
Preferred Stock, Authorized	5,000,000
Junior participating preferred Stock, Authorized	2,000,000
Preferred Stock, Shares Outstanding	0
Junior Preferred Stock, Shares Outstanding	0

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PreferredStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant