Summary of Significant Accounting Policies - Adoption of ASU 2016-02 (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property and equipment, net	$ 547,056	$ 379,268	$ 606,977
Operating lease right-of-use assets	756,716	524,082
Other noncurrent assets	13,951	12,012	18,826
Other liabilities		4,392	160,388
Other current liabilities	200,502	118,371	127,995
Lease financing obligation, net of current portion	0	0	183,056
Operating lease liabilities	899,867	636,385
Accumulated deficit	$ (1,735,201)	(1,080,839)	$ (1,082,689)
ASU 2016-02 Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property and equipment, net		(227,709)
Operating lease right-of-use assets		524,082
Other noncurrent assets		(6,814)
Other liabilities		(155,996)
Other current liabilities		(9,624)
Lease financing obligation, net of current portion		(183,056)
Operating lease liabilities		636,385
Accumulated deficit		$ 1,850