Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 13,800	$ 12,800
Unrecognized tax benefits	0
Accrued interest or penalties related to uncertain tax positions	0	$ 0
Federal [Member]
Income Taxes [Line Items]
Net operating losses	329,600
Net operating loss carryforwards, subject to expiration	$ 228,200
Net operating loss carryforwards, expiration date	Dec. 31, 2037
Net operating loss carryforwards, not subject to expiration	$ 101,400
Federal [Member] | Research and Development [Member]
Income Taxes [Line Items]
Credit carryforward	$ 5,500
Credit carryforward, expiration date	Dec. 31, 2039
State [Member]
Income Taxes [Line Items]
Net operating losses	$ 292,400
Net operating loss carryforwards, subject to expiration	$ 288,000
Net operating loss carryforwards, expiration date	Dec. 31, 2039
Net operating loss carryforwards, not subject to expiration	$ 4,400
State [Member] | Research and Development [Member]
Income Taxes [Line Items]
Credit carryforward	$ 3,600
Credit carryforward, expiration date	Dec. 31, 2034