Summary of Significant Accounting Policies - Accounting Pronouncements (Details) - USD ($) $ in Thousands		9 Months Ended
	Jan. 01, 2019	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 24,807
Operating lease liabilities		33,361
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 28,200
Derecognition of deferred rent	9,500
Derecognition of prepaid rent	700
Operating lease liabilities	$ 37,000
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment upon adoption of ASU 2018-07		$ (185)