XML 55 R41.htm IDEA: XBRL DOCUMENT v3.8.0.1
Summary of Significant Accounting Policies - Schedule of Estimated Useful Life of Property and Equipment (Detail)
12 Months Ended
Dec. 31, 2017
Leasehold improvements [Member]  
Property, Plant and Equipment [Line Items]  
Estimated useful lives Shorter of estimated useful life or term of lease
Furniture and equipment [Member] | Minimum [Member]  
Property, Plant and Equipment [Line Items]  
Estimated useful lives 3 years
Furniture and equipment [Member] | Maximum [Member]  
Property, Plant and Equipment [Line Items]  
Estimated useful lives 10 years
Internal-use software [Member] | Minimum [Member]  
Property, Plant and Equipment [Line Items]  
Estimated useful lives 3 years
Internal-use software [Member] | Maximum [Member]  
Property, Plant and Equipment [Line Items]  
Estimated useful lives 7 years