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Available-for-Sale Investments - Additional Information (Detail) $ in Millions	Sep. 30, 2019 USD ($) Investment Security	Dec. 31, 2018 USD ($) Investment
Investments Debt And Equity Securities [Abstract]
Number of investments in unrealized loss position	4	37
Number of investments in unrealized loss position, more than twelve months	0	0
Aggregate fair value of securities in unrealized loss position | $	$ 9.5	$ 96.5
Number of securities with other than temporary impairment | Security	0

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Other than temporary impairment losses investments number debt securities available for sale.

+ References

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

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-Publisher FASB
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-Publisher FASB
-Name Accounting Standards Codification
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-Section 55
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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

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