Summary of Significant Accounting Policies - Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2017
Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible asset, estimated period of benefit	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible asset, estimated period of benefit	15 years
Maximum | Capitalized software development
Finite-Lived Intangible Assets [Line Items]
Intangible asset, estimated period of benefit	2 years