Basis of Presentation and Accounting Policies - Additional Information (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) segment	Dec. 31, 2018	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments | segment	1
Length of lease			15 years
Cumulative effect adjustment to accumulated deficit			$ (40,310)	$ 9,229
Operating lease assets	$ 60,929		61,674
Present value of lease liabilities	$ 71,177
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit			(40,310)	$ 33,349
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets			61,674
Present value of lease liabilities			71,900
Accounting Standards Update 2016-02 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit			$ (40,300)
Building
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life	40 years	40 years