CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
REVENUE	$ 32,713	$ 26,881
COSTS AND EXPENSES:
FI Share and other third-party costs	21,420	16,677
Delivery costs	1,943	1,553
Sales and marketing expense	8,216	7,232
Research and development expense	3,459	3,013
General and administration expense	6,582	4,689
Depreciation and amortization expense	910	765
Total costs and expenses	42,530	33,929
OPERATING LOSS	(9,817)	(7,048)
OTHER INCOME (EXPENSE):
Interest expense, net	(1,749)	(2,644)
Change in fair value of warrant liabilities, net	(9,172)	(327)
Change in fair value of convertible promissory notes	0	(383)
Change in fair value of convertible promissory notes—related parties	0	(2,223)
Other income, net	683	162
Total other expense	(10,238)	(5,415)
LOSS BEFORE INCOME TAXES	(20,055)	(12,463)
INCOME TAX BENEFIT	0	0
NET LOSS	(20,055)	(12,463)
Adjustments to the carrying value of redeemable convertible preferred stock	(157)	(244)
Net loss attributable to common stockholders	$ (20,212)	$ (12,707)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (1.54)	$ (4.80)
Weighted-average common shares outstanding, basic and diluted (in shares)	13,093	2,645