Additions made to capitalized computer software costs during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

Name:	us-gaap_CapitalizedComputerSoftwareAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Summary of Significant Accounting Policies - Software Development Costs (Details) - Capitalized Technology - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Software Development Costs
Software development costs capitalized	$ 0	$ 0	$ 0
Minimum
Software Development Costs
Estimated useful lives of assets	2 years
Maximum
Software Development Costs
Estimated useful lives of assets	5 years