Investment in Securities - Additional Information (Detail) - USD ($)	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Securities transferred from held-to-maturity to available-for-sale	$ 157,939,000,000	$ 34,850,000
Realized loss, transferred securities	$ 0	$ 0

Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27405-111563

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