Stockholders' Equity - ESPP Activity (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Number of shares issued (in thousands)	130	164	202
Weighted average price	$ 136.73	$ 96.95	$ 59.93

Number of shares issued during the period as a result of an employee stock purchase plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Name:	us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration