Securities Available for Sale - Additional Information (Detail) - DebtInstrument	6 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Number of debt securities with unrealized losses	33	59
Percentage of depreciation from amortized cost bases	1.50%	3.60%

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=82897076&loc=d3e27290-111563

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Balance Type:	na
Period Type:	duration