Japanese Yen Deposits - Additional Information (Detail)	2 Months Ended	3 Months Ended
Dec. 31, 2018 JPY (¥)	Mar. 31, 2019 USD ($)	Mar. 31, 2019 JPY (¥)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 JPY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 JPY (¥)
Cash And Cash Equivalents [Abstract]
Principal deposits	¥ 4,776,165,855	$ 244,269,613	¥ 26,249,243,674	$ 79,698,689
Principal redemptions	0	230,772,038	25,758,963,088	$ 8,852,936
Withdrawals (to pay expenses)	¥ 12,310,233		¥ 34,411,854
Deposits, interest bearing		$ 176,724,388			¥ 19,560,738,879	$ 174,131,797	¥ 19,104,870,147
Annual nominal rate		(0.10%)	(0.10%)

The interest rate for investments that have an interest rate. For fixed rate investments, this indicates the fixed interest rate. If the investment has a variable interest rate, the rate stated here may be the rate that is currently relevant. In this case the "Investment, Interest Rate is Current Rate for Variable Rate Investment Flag", "Investment, Interest Rate is Discount Rate at Purchase Flag", "Investment, Interest Rate Reflects Current Yield Flag" should be used. If one of these flags are not appropriate to explain the interest rate that is indicated, then a new flag should be added or an explanation should be included in "Investment, Additional Information".

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

+ Details

Name:	invest_InvestmentInterestRate
Namespace Prefix:	invest_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_Cash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total amount of cash paid for operating activities during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (d)-(g)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForOperatingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow for reacquisition of callable preferred stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

+ Details

Name:	us-gaap_PaymentsForRepurchaseOfRedeemablePreferredStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from issuance of preferred stock that is classified as callable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

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