SUMMARY OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) shares	Sep. 30, 2016 Customer $ / shares	Sep. 30, 2015 Customer $ / shares	Sep. 30, 2016 USD ($) Customer $ / shares shares	Sep. 30, 2015 USD ($) Customer $ / shares	Dec. 31, 2015 Customer $ / shares
Summary Of Significant Accounting Policies [Line Items]
Proceeds from initial public offering | $	$ 93,093			$ 0	$ 93,093
Underwriting discounts and commissions | $	7,007
Paid and unpaid offering expenses | $	$ 4,024
Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Number of Customers | Customer				1		1
Accounts Receivable | Customer Concentration Risk
Summary Of Significant Accounting Policies [Line Items]
Concentration risk (as a percent)				19.00%		18.00%
Revenue
Summary Of Significant Accounting Policies [Line Items]
Number of Customers | Customer		0	0	0	0
Common Class A
Summary Of Significant Accounting Policies [Line Items]
Common stock, par value (in dollars per share) | $ / shares		$ 0.000004	$ 0.000004	$ 0.000004	$ 0.000004	$ 0.000004
Common Class A | IPO
Summary Of Significant Accounting Policies [Line Items]
Issuance of common stock upon initial public offering, net of offering costs (in shares)	7,150,000
Stock issued, public offering price (in dollars per share) | $ / shares			14.00		14.00
Common Class B
Summary Of Significant Accounting Policies [Line Items]
Common stock, par value (in dollars per share) | $ / shares		$ 0.000004	$ 0.000004	$ 0.000004	$ 0.000004	$ 0.000004
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)	20,673,680			20,673,680
Reclassifications of common stock outstanding (in shares)	11,305,355
Common Class B | IPO
Summary Of Significant Accounting Policies [Line Items]
Reclassifications of common stock outstanding (in shares)				11,305,355