Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Segment
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Significant Accounting Policies [Line Items]      
Amortization period description The amortization period begins with the first month of availability on our service.    
Number of reporting unit | Segment 1    
Impairment of goodwill $ 0 $ 0 $ 0
Impairment of long-lived assets 0 0 0
Advertising expense $ 25,700,000 $ 13,200,000 $ 5,500,000
Defined contribution plan percentage employee's matching contribution 50.00%    
Defined contribution plan maximum annual matching contribution amount $ 1,500    
Common stock shares excluded from computation of dilutive earnings per share | shares 57,000 910,000 954,000
Impairment charges on cost method investments $ 0 $ 0 $ 0
Defined Contribution Plan 401 (k) [Member]      
Significant Accounting Policies [Line Items]      
Defined contribution plan annual matching contribution amount $ 100,000 $ 82,000 $ 56,000
Website Development Costs and Other Software [Member]      
Significant Accounting Policies [Line Items]      
Estimated useful life of property and equipment 3 years    
Minimum [Member]      
Significant Accounting Policies [Line Items]      
Estimated useful life of property and equipment 3 years    
License period or estimated useful life of media library 12 months    
Maximum [Member]      
Significant Accounting Policies [Line Items]      
Estimated useful life of property and equipment 45 years    
License period or estimated useful life of media library 90 months