Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
License revenue, and other	$ 18,821,953		$ 20,155,286
Type of Revenue [Extensible List]	arpo:LicenseRevenueAndOtherMember		arpo:LicenseRevenueAndOtherMember
Operating expenses
Research and development	$ 4,346,381	$ 2,942,170	$ 12,604,125	$ 8,366,869
General and administrative	3,277,535	1,814,068	9,866,227	6,732,816
Total operating expenses	7,623,916	4,756,238	22,470,352	15,099,685
Income (loss) from operations	11,198,037	(4,756,238)	(2,315,066)	(15,099,685)
Grant income	6,394	46,824	6,394	93,720
Interest income (expense), net	333,047	59,847	430,626	(159,612)
Total other income (expense)	339,441	106,671	437,020	(65,892)
Net and comprehensive income (loss)	11,537,478	(4,649,567)	(1,878,046)	(15,165,577)
Reconciliation of net income (loss) attributable to common stockholders:
Net and comprehensive income (loss)	11,537,478	(4,649,567)	(1,878,046)	(15,165,577)
Adjustment of redeemable convertible preferred stock to redemption value				(943,297)
Net income (loss) attributable to common stockholders	$ 11,537,478	$ (4,649,567)	$ (1,878,046)	$ (16,108,874)
Net income (loss) per share
Basic and diluted	$ 0.28	$ (0.17)	$ (0.06)	$ (0.81)
Weighted average number of common shares used in computing net income (loss) per share
Basic	40,527,722	26,926,673	31,687,434	19,889,984
Diluted	40,961,620	26,926,673	31,687,434	19,889,984