3. Amortized Cost and Fair Value of Debt Securities (Details) $ in Millions	Sep. 30, 2019 USD ($)
Fair Value Disclosures [Abstract]
Mature in less than one year	$ 139.9
Mature in one to five years	168.3
Mature in more than five years	60.2
Total Amortized Cost	368.4
Mature in less than one year	140.0
Mature in one to five years	169.4
Mature in more than five years	61.5
Estimated Fair Value	$ 370.9

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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