Significant Accounting Policies - Estimated Useful Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2017
Computer equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	3 years
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	3 years
Office equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	3 years
Software [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of the assets	3 years