Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax provisions or benefits	$ 0		$ 0	$ 0	$ 0
Alternative minimum tax payable	0			$ 0		$ 800,000
Alternative minimum tax paid		$ 800,000
Alternative minimum tax receivable						$ 800,000
Federal tax at statutory rate				21.00%		35.00%
Tax Cuts and Jobs Act of 2017 change in tax rate reduction in deferred tax asset and corresponding valuation allowance						$ 43,000,000
Other Assets
Income Tax Disclosure [Line Items]
Alternative minimum tax receivable	$ 800,000			$ 800,000