Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Product Information [Line Items]
Operating lease ROU assets	$ 53,839		$ 0
Current operating lease liabilities	10,575		0
Noncurrent operating lease liabilities	$ 50,965		$ 0
Effect of adopting accounting principle in period of adoption		$ 4,646		$ (3,076)
Accumulated Deficit
Product Information [Line Items]
Effect of adopting accounting principle in period of adoption		4,646		$ (3,076)
ASC 842
Product Information [Line Items]
Operating lease ROU assets		59,400
Current operating lease liabilities		11,000
Noncurrent operating lease liabilities		57,300
ASC 842 | Accumulated Deficit
Product Information [Line Items]
Effect of adopting accounting principle in period of adoption		$ 4,600