Securities Available for Sale - Additional Information (Detail) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($) DebtInstrument	Sep. 30, 2018 USD ($)	Sep. 30, 2019 DebtInstrument	Sep. 30, 2018 USD ($)	Dec. 31, 2018 DebtInstrument
Investments, Debt and Equity Securities [Abstract]
Number of debt securities with unrealized losses \| DebtInstrument	22		22		59
Percentage of depreciation from amortized cost bases			0.70%		3.60%
Proceeds from sales of securities available-for-sale \| $	$ 0	$ 0		$ 14,392

This item represents the default rate of the underlying assets in the security that were considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than-temporarily impaired.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-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

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration