Stockholders' Equity - RSU and PSU award activity (Details) - $ / shares	1 Months Ended				12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Jun. 30, 2018	Dec. 31, 2019
Shares Subject to Outstanding Options, Shares
Outstanding at the beginning of the period (in shares)					2,043,337
Outstanding at the end of the period (in shares)					2,602,376
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)					$ 80.35
Outstanding at the end of the period (in dollars per share)					$ 79.69
Restricted Stock Units (RSUs)
Shares Subject to Outstanding Options, Shares
Granted (in shares)				190,000	1,154,361
Released (in shares)					(592,736)
Cancelled (in shares)					(184,214)
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Granted (in dollars per share)					$ 83.23
Released (in dollars per share)					87.70
Cancelled (in dollars per share)					$ 83.23
Performance Stock Units (PSUs)
Shares Subject to Outstanding Options, Shares
Granted (in shares)	86,975	100,000	77,243	446,500	233,467
Released (in shares)					(13,325)
Cancelled (in shares)					(38,514)
Shares Subject to Outstanding Options, Weighted Average Exercise Price
Granted (in dollars per share)					$ 79.37
Released (in dollars per share)					68.62
Cancelled (in dollars per share)					$ 66.16