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) - position
9 Months Ended
Sep. 30, 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 3,200    
Total unrealized investment positions 3,954    
RxAdvance      
Schedule Of Investments And Restricted Deposits By Type [Line Items]      
Equity method investment, percentage   28.00% 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 10 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%