Income Taxes - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	May 30, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards		$ 27,988	$ 27,988
Operating Loss Carryforwards Expiration Period			2027
Operating loss carryforwards expiration in year one		136,840	$ 136,840
Operating loss carryforwards expiration in year two		102,927	102,927
Operating loss carryforwards expiration in year three		70,319	70,319
Operating loss carryforwards expiration in year four		3,763	3,763
Operating loss carryforwards expiration in year five		77,074	$ 77,074
Statutory federal income tax rate			21.00%	35.00%
Excess AMT credit carryforwards refundable rate			50.00%
AMT credit carryforward		9,132	$ 9,132	$ 9,133
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount		8,503	40,833
Tax Year 2017 | Arlington County, Virginia
Income Tax Disclosure [Line Items]
Tax assessment received for business, professional and occupation license tax	$ 9,380
Capital Loss Carryforward
Income Tax Disclosure [Line Items]
Tax Credit Carryforward, Amount		$ 390,923	$ 390,923