Financial Instruments (Details Textual 1)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Financial Instruments (Textual)
Original maturities of commercial paper and short-term debt securities	less than 90 days
Overnight reverse repurchase agreements, percent of total assets		0.71%
Average maturity of marketable securities, months	12 months	16 months

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration