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Cash Equivalents and Investments (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) investment	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) investment	Sep. 30, 2017 USD ($)
Investments Debt And Equity Securities [Abstract]
Realized gains (losses) recognized on the sale or maturity of available-for-sale securities | $	$ 0	$ 0	$ 0	$ 0
Securities in continuous unrealized loss position for more than one year | investment	0		0

X

- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

No definition available.

+ Details

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X

- Definition

Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- References

No definition available.

+ Details

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