CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 48,730	$ 35,570	$ 84,718	$ 68,283
Costs and expenses:
FI Share and other third-party costs	27,620	19,747	46,624	41,167
Delivery costs	3,370	2,559	6,616	4,502
Sales and marketing expense	11,047	10,247	20,384	18,463
Research and development expense	2,782	4,888	5,723	8,347
General and administration expense	8,340	8,979	15,340	15,561
Depreciation and amortization expense	1,053	784	2,014	1,694
Total costs and expenses	54,212	47,204	96,701	89,734
Operating loss	(5,482)	(11,634)	(11,983)	(21,451)
Other (expense) income:
Interest expense, net	(338)	(992)	(642)	(2,741)
Change in fair value of warrant liabilities, net	0	1,611	0	(7,561)
Other expense, net	(690)	(2,038)	(199)	(1,355)
Total other expense	(1,028)	(1,419)	(841)	(11,657)
Loss before income taxes	(6,510)	(13,053)	(12,824)	(33,108)
Income tax benefit	0	0	0	0
Net loss	(6,510)	(13,053)	(12,824)	(33,108)
Adjustments to the carrying value of preferred stock	0	0	0	(157)
Net loss attributable to common stockholders	$ (6,510)	$ (13,053)	$ (12,824)	$ (33,265)
Net loss per share attributable to common stockholders, basic and diluted (in USD per share)	$ (0.29)	$ (0.64)	$ (0.57)	$ (1.99)
Weighted-average common shares outstanding, basic and diluted (in shares)	22,731	20,300	22,618	16,716