CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Cash flows from operating activities:    
Net loss $ (20,594) $ (12,439)
Adjustments to reconcile net loss to net cash used in operating activities:    
Depreciation and amortization expense 1,905 1,658
Stock-based compensation expense 2,389 2,207
Provisions for doubtful accounts 19 (155)
Non-cash interest expense 9 1
Change in fair value of warrant liability 2,881 (126)
Deferred income taxes 4  
Changes in operating assets and liabilities:    
Accounts receivable 24,031 14,314
Prepaid expenses and other assets (1,861) (2,469)
Deferred commissions (494) (154)
Accounts payable 25 1,050
Accrued expenses (2,305) (6,060)
Deferred revenue (6,703) (4,596)
Deferred rent (82) (206)
Other long-term liabilities (1) (67)
Net cash used in operating activities (777) (7,042)
Cash flows from investing activities:    
Purchases of property and equipment (1,495) (828)
Capitalization of internal-use software costs (293) (204)
Net cash used in investing activities (1,788) (1,032)
Cash flows from financing activities:    
Proceeds from exercise of stock options 1,065 557
Payments of deferred financing costs (47) (76)
Payments of initial public offering costs (840) (2)
Net cash provided by financing activities 178 479
Net decrease in cash and cash equivalents (2,387) (7,595)
Cash and cash equivalents at beginning of period 36,073 51,503
Cash and cash equivalents at end of period 33,686 43,908
Supplemental disclosure of noncash investing and financing activities:    
Accretion of preferred stock to redemption value 40,039 11,647
Additions to property and equipment included in accounts payable at period end 353 $ 1,267
Deferred offering costs included in accounts payable at period end $ 546