Cash Equivalents and Investments (Details)	3 Months Ended
Mar. 31, 2018 USD ($) investment	Mar. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Realized gains (losses) recognized on the sale or maturity of available-for-sale securities \| $	$ 0	$ 0
Securities in continuous unrealized loss position for more than one year \| investment	0
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Investments, remaining maturity	1 year 6 months

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration