Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Current income tax expense			$ 0	$ 0
Deferred income tax expense		$ 0	0	0
Increase (decrease) in valuation allowance, deferred tax assets		(4,900,000)	56,400,000
Deferred capitalized start up expense net of amortization		800,000	900,000
Deferred income tax amortization		$ 1,100,000	1,000,000
NOL and R&D tax credit carry forward expiration year		2037
Changes in ownership interest rate period		3 years
Cumulative changes in ownership interest of shareholders		50.00%
Unrecognized tax benefits		$ 0	0	0
Income tax penalties and interest accrued associated with unrecognized tax benefits		0	0	0
Income tax penalties and interest expense associated with unrecognized tax benefits		$ 0	$ 0	$ 0
Federal tax at statutory rate		34.00%	34.00%	34.00%
Tax Cuts and Jobs Act of 2017 change in tax rate reduction in deferred tax asset and corresponding valuation allowance		$ 43,000,000
Maximum
Income Tax Disclosure [Line Items]
Federal tax at statutory rate		35.00%
Scenario, Plan
Income Tax Disclosure [Line Items]
Federal tax at statutory rate	21.00%
Net Operating Loss
Income Tax Disclosure [Line Items]
Future offset taxable income			$ 170,000,000
ASU 2016-09 | Net Operating Loss
Income Tax Disclosure [Line Items]
Increase (decrease) in valuation allowance, deferred tax assets		$ 1,300,000
Impact of restatement on opening retained earnings, net of tax		0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 179,700,000	234,500,000
Operating Loss Carryforwards Expiration Year		2036
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 74,600,000	$ 103,900,000
Operating Loss Carryforwards Expiration Year		2036
Federal and State | Earliest Tax Year
Income Tax Disclosure [Line Items]
Tax years remain open and subject to examination		2014
Federal and State | Latest Tax Year
Income Tax Disclosure [Line Items]
Tax years remain open and subject to examination		2016
Federal and State | Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 25,700,000
Other Assets
Income Tax Disclosure [Line Items]
Alternative minimum tax receivable		1,000,000
Accrued Expenses
Income Tax Disclosure [Line Items]
Alternative minimum tax payable		$ 1,000,000