Stockholders' Equity - Option activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	6 Months Ended	12 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares Subject to Outstanding Options, Shares
Outstanding at the beginning of the period (in shares)			12,632,657
Options granted (in shares)			2,256,146
Options exercised (in shares)			(2,230,588)
Options cancelled (in shares)			(542,927)
Outstanding at the end of the period (in shares)			12,115,288	12,632,657
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 81.42
Options granted (in dollars per share)			92.82
Options exercised (in dollars per share)			52.78
Options cancelled (in dollars per share)			92.66
Outstanding at the end of the period (in dollars per share)			$ 88.31	$ 81.42
Termination period	10 years	7 years
Vesting period	4 years	3 years
Stock option, other disclosures
Options exercisable and vested (in shares)			6,732,942	6,896,492	7,194,171
Intrinsic value of options exercised			$ 87.5	$ 113.8	$ 73.9
Intrinsic value of options outstanding			86.3
Intrinsic value of vested options			$ 84.3
Vesting after one year
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Vesting period	1 year	1 year
Vesting Percentage	25.00%	33.00%
Remainder vesting
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Vesting period	36 months	24 months