Fair Value Measurements - Narrative (Details) $ in Millions	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position, accumulated loss	$ 3.9
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale marketable securities, continuous unrealized loss position for more than 12 months	$ 462.4

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant