Commitments and Contingencies - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) wharehouse	Dec. 31, 2017 USD ($) wharehouse	Dec. 31, 2016 USD ($)
Other Commitments [Line Items]
Rent expense under operating leases	$ 63,800	$ 45,200	$ 33,600
Letters of credit outstanding, amount	26,800	15,300
Minimum sublease rentals	3,400
Lease financing obligations, net of current portion	183,056	82,580
Land lease expense	2,700	900	100
Financing obligation, interest expense	12,000	$ 6,900	$ 1,400
Financing obligation, future minimum commitments due, principal	75,600
Financing obligation, future minimum commitments due, interest	$ 22,100
Warehouse Lease Agreement
Other Commitments [Line Items]
Warehouse lease arrangements | wharehouse	3	2
Warehouse Lease Agreement | Warehouse Lease Arrangement, One, 2018
Other Commitments [Line Items]
Letters of credit outstanding, amount	$ 2,500
Warehouse Lease Agreement | Warehouse Lease Arrangement One, 2017
Other Commitments [Line Items]
Letters of credit outstanding, amount		$ 800
Warehouse Lease Agreement | Warehouse Lease Arrangement, Two, 2017
Other Commitments [Line Items]
Letters of credit outstanding, amount		1,000
Warehouse Lease Agreement | Warehouse Lease Arrangement One and Two, 2017
Other Commitments [Line Items]
Lease financing obligations, net of current portion	$ 101,000	$ 53,800