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Short-term and Long-term Investments, Restricted Deposits - Narrative (Details) - position	12 Months Ended
	Dec. 31, 2018	May 31, 2018	Mar. 31, 2018
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Positions from which gross unrealized losses were generated	3,096
Total number of positions	4,190
RxAdvance
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Equity method investment, ownership percentage		28.00%	25.00%
Commercial mortgage- backed securities
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Investments that carry rating of A A plus, weighted average, duration	3 years 8 months
External Credit Rating, Investment Grade | Rated Securities
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Percentage of investment grade investments rated by nationally recognized statistical rating organizations	96.00%

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Investments Recorded At Fair Value That Carry Rating Of A A Plus, Weighted Average, Duration

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