Investment in Securities, Investments Classified as Available for Sale in Unrealized Loss Position (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($) Investment	Sep. 30, 2017 USD ($) Investment	Dec. 31, 2017 Investment
Available-for-sale securities in continuous unrealized loss position [Abstract]
Number of investment holding in loss positions \| Investment	0	0	0
Losses on available for sale securities deemed to be other than temporary \| $	$ 0	$ 0

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Name:	us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant