Assets Held for Sale - Additional Information (Details) $ in Thousands			9 Months Ended	12 Months Ended
	Aug. 23, 2018 USD ($)	Jul. 19, 2018 USD ($)	Sep. 30, 2018	Dec. 31, 2016 Building	Dec. 31, 2017 USD ($)
Long Lived Assets Held For Sale [Line Items]
Carrying value of facilities					$ 409
Assets held for sale
Long Lived Assets Held For Sale [Line Items]
Number of property held for sale | Building				1
Disposed of by Sale | New York Facilities
Long Lived Assets Held For Sale [Line Items]
Changes to plan of facilities sale, description			Pursuant to an agreement entered into by the Company, as of September 12, 2017, with 26 W. 56 LLC, the Company closed on the sale of its New York facilities on July 19, 2018 with a carrying value of $0.4 million for $14.0 million, exclusive of closing costs. The Company recognized a gain on the sale of the New York facilities of $12.5 million. Additionally, the sale of the New York facilities resulted in net proceeds of $10.4 million to the Company, as defined by the Indenture governing the Notes, which is calculated differently than the recognized gain for financial reporting purposes. In order to arrive at net proceeds, as defined by the Indenture, the Company is permitted to hold back certain amounts related to taxes, relocation expenses and capital expenditures that are expected to become payable in the future. The net proceeds of $10.4 million was used to repay a portion of the Notes on August 23, 2018.
Carrying value of facilities		$ 400
Agreement entered date for sale of facilities			Sep. 12, 2017
Gain on sale of property		12,500
Purchase price of facilities, excluding closing costs		$ 14,000
Net proceeds from sale of facility	$ 10,400