Description of Business and Significant Accounting Policies - Software Development Costs Incurred to Stock-Based Compensation (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)
Description Of Business And Significant Accounting Policies [Line Items]
Capitalized development costs of software to be sold or marketed	$ 0
Capitalized development costs of software for internal use	$ 0
Stock-based compensation, vesting term (in years)	4 years
Computers and appliances
Description Of Business And Significant Accounting Policies [Line Items]
Property plant and equipment useful life	3 years
Furniture and fixtures
Description Of Business And Significant Accounting Policies [Line Items]
Property plant and equipment useful life	5 years