Summary of Significant Accounting Policies - Leases (Details)	12 Months Ended
Dec. 31, 2018
Operating Leased Assets [Line Items]
Short-term office lease, maximum term	1 year
Minimum
Operating Leased Assets [Line Items]
Term of lease contract	3 years
Maximum
Operating Leased Assets [Line Items]
Term of lease contract	7 years

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant