Marketable Securities - Narrative (Details)	6 Months Ended
	Jun. 30, 2019
Short-term Marketable Securities | Minimum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	1 month
Short-term Marketable Securities | Maximum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	12 months
Long-term Marketable Securities | Minimum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	13 months
Long-term Marketable Securities | Maximum
Line of Credit Facility [Line Items]
Marketable securities, remaining maturities (in months)	34 months