Quarterly report pursuant to Section 13 or 15(d)

Short-term and Long-term Investments, Restricted Deposits - (Narrative) (Details)

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Short-term and Long-term Investments, Restricted Deposits - (Narrative) (Details)
3 Months Ended
Mar. 31, 2018
position
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Positions from which gross unrealized losses were generated 2,714
Total unrealized investment positions 3,564
RxAdvance  
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Equity method investment, percentage 25.00%
Commercial mortgage-backed securities  
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Investments recorded at fair value that carry rating of AA Plus, weighted average (in years) 3 years 11 months
Rated Securities | External Credit Rating, Investment Grade  
Schedule Of Investments And Restricted Deposits By Type [Line Items]  
Percentage of investments in rated securities carry an investment grade rating by nationally recognized statistical rating organizations 96.00%