Contractual Maturities of Investments in Debt Securities Held (Detail) $ in Thousands	Sep. 30, 2018 USD ($)
Schedule of Available-for-sale Securities
Due within one year, cost	$ 418,554
Due after 1 year through 5 years, cost	11,477
Due after 5 years through 10 years, cost	14,906
Due after 10 years, cost	40,467
Total, cost	485,404
Due within one year, fair market value	418,410
Due after 1 year through 5 years, fair market value	11,368
Due after 5 years through 10 years, fair market value	13,949
Due after 10 years, fair maket value	38,925
Total, fair market value	$ 482,652

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth fiscal year through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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