Schedule of Net Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax asset (liability)
Net operating loss carryforwards	$ 41,152,000	$ 27,999,000	$ 23,391,000
Deferred tax asset (liability) Non-deductible accrued expenses	245,000	248,000	358,000
Deferred rent	148,000	49,000	1,000
Deferred revenue		38,000	69,000
Stock compensation expense	899,000	387,000	101,000
Depreciation differences	(125,000)	(18,000)	(13,000)
Charitable contributions	6,000	6,000	6,000
Valuation allowance	(49,563,000)	(32,670,000)	(25,446,000)
Federal
Deferred tax asset (liability)
Net operating loss carryforwards	41,000,000
Tax credits	6,481,000	3,437,000	1,232,000
State
Deferred tax asset (liability)
Net operating loss carryforwards	150,000
Tax credits	$ 757,000	$ 524,000	$ 301,000