Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, shares in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2015 USD ($) $ / shares shares	May 31, 2014 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) Customer $ / shares	Dec. 31, 2015 USD ($) Customer	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Share price (usd per share) | $ / shares			$ 21.20
Proceeds from initial public offering, net of underwriting discounts and commissions and other offering expenses			$ 0	$ 0	$ 103,090,000
Number of shares of common stock issued upon automatic conversion of convertible preferred stock (in shares) | shares		34.3
Proceeds from follow-on public offering, net of issuance costs			0	190,094,000	0
Restricted cash			2,500,000	1,300,000
Cash collateral			$ 1,100,000
Weighted average useful life of capitalized internal use software			3 years 3 months 18 days
Impairment of goodwill			$ 0	0
Impairment of long lived asset			$ 0	0
Service condition for performance awards			4 years
Future period share-based compensation expense			$ 173,400,000
Future period share-based compensation expense, period to recognized			2 years 8 months 2 days
Advertising expense			$ 23,900,000	$ 16,500,000	12,700,000
Grant proceeds			$ 1,200,000
Customer Concentration Risk | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer			0	0
Customer Concentration Risk | Accounts Receivable | Maximum
Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenue or receivables			10.00%	10.00%
Customer Concentration Risk | Revenue
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer			0	0
Customer Concentration Risk | Revenue | Maximum
Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenue or receivables			10.00%	10.00%
Performance Awards
Summary Of Significant Accounting Policies [Line Items]
Service condition for performance awards			4 years
Share-based compensation expense			$ 2,800,000	$ 6,100,000	$ 12,700,000
Charitable Donation
Summary Of Significant Accounting Policies [Line Items]
Restricted cash			1,000,000	900,000
Leased Building
Summary Of Significant Accounting Policies [Line Items]
Restricted cash				$ 400,000
IPO
Summary Of Significant Accounting Policies [Line Items]
Shares of common stock sold in initial public offering (in shares) | shares		12.8
Share price (usd per share) | $ / shares		$ 9.00
Proceeds from initial public offering, net of underwriting discounts and commissions and other offering expenses		$ 103,100,000
Underwriting discounts and commission on IPO		8,100,000
Offering expenses		$ 3,800,000
Number of shares of common stock issued upon automatic conversion of convertible preferred stock (in shares) | shares		34.3
Follow On Public Offering
Summary Of Significant Accounting Policies [Line Items]
Shares of common stock sold in initial public offering (in shares) | shares	8.8
Share price (usd per share) | $ / shares	$ 22.75
Underwriting discounts and commission on IPO	$ 8,700,000
Offering expenses	900,000
Proceeds from follow-on public offering, net of issuance costs	$ 190,100,000
Prior to IPO | Performance Awards
Summary Of Significant Accounting Policies [Line Items]
Share-based compensation expense			$ 0