Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
U.S. statutory tax rate	21.00%
Provision for income taxes	$ 44,000	$ 0	$ 0
Benefit recognized for net operating loss carryforwards	0
Benefit recognized for other deferred tax assets	0
Increase (decrease) in valuation allowance	21,700,000	(600,000)
Net operating loss carryforwards, federal	206,700,000
Net operating loss carryforwards, state	107,400,000
Tax credit carryforward	3,700,000
Tax credit carryforwards available to reduce future taxable income	$ 2,400,000
Tax credit carryforwards expiration beginning year	2028
Unrecognized tax benefit	$ 1,500,000	900,000	$ 600,000
Accrual for interest or penalties related to unrecognized tax benefits	$ 0	$ 0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carry forwards expiration year	2027
State
Income Tax Disclosure [Line Items]
Net operating loss carry forwards expiration year	2019