Commitments and Contingencies - Indemnifications (Details) - Indemnifications	6 Months Ended
Jun. 30, 2018 claim
Indemnifications
Number of claims pending	0
Number of new claims	0

The total number of new claims filed pertaining to a loss contingency during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration