Balance Sheet Components - Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 915,506		$ 915,506		$ 760,899
Increase in deferred revenue	22,729	$ 18,983	154,607	$ 98,101
Gift Cards and Other Prepaid Memberships
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 916,000		916,000
Increase in deferred revenue			$ 155,000