Leases - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) lease	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease expense	$ 31,800	$ 17,500	$ 86,800	$ 48,100
Operating leases not yet commenced			332,600
Letter of credit issued as security for lease agreements	46,400		46,400		$ 26,800
Lease financing obligation, net of current portion	$ 0		$ 0		$ 183,056	$ 0
Property Lease Guarantee
Lessee, Lease, Description [Line Items]
Number of warehouse lease arrangements | lease					3
Lease financing obligation, net of current portion					$ 101,000
Property Lease Guarantee | Warehouse Lease Arrangement, One 2018
Lessee, Lease, Description [Line Items]
Letter of credit issued as security for lease agreements					$ 2,500
Minimum
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, term of contract	2 years		2 years
Maximum
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, term of contract	15 years		15 years