Note 11 - Fair Value Measurement and Disclosure - Estimated Fair Values of Financial Instruments (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Reported Value Measurement [Member] \| Non-Interest Bearing Deposits [Member]
Deposits	$ 10,285,561	$ 10,325,832
Reported Value Measurement [Member] \| Interest Bearing Deposits, Liabilities [Member]
Deposits	221,601,449	166,409,076
Reported Value Measurement [Member]
Cash and cash equivalents	4,469,007	7,135,719
Time deposits	250,000	250,000
Federal funds sold	54,351,000	1,604,000
Securities	44,902,860	48,343,028
Accrued interest receivable	800,249	775,641
Net loans	154,943,940	140,110,201
Loans held for sale	710,700
Mortgage servicing rights	328,360	285,927
Accrued interest payable	1,697	394
FHLB advances	8,630,697	2,139,117
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| Non-Interest Bearing Deposits [Member]
Deposits	10,285,561	10,325,832
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| Interest Bearing Deposits, Liabilities [Member]
Deposits
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	4,469,007	7,135,719
Time deposits	250,000	250,000
Federal funds sold	54,351,000	1,604,000
Securities
Accrued interest receivable	800,249	775,641
Net loans
Loans held for sale	710,700
Mortgage servicing rights
Accrued interest payable	1,697	394
FHLB advances
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Non-Interest Bearing Deposits [Member]
Deposits
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Bearing Deposits, Liabilities [Member]
Deposits
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents
Time deposits
Federal funds sold
Securities	44,149,539	46,984,907
Accrued interest receivable
Net loans
Loans held for sale
Mortgage servicing rights
Accrued interest payable
FHLB advances	8,630,697	2,139,117
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member] \| Non-Interest Bearing Deposits [Member]
Deposits
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Bearing Deposits, Liabilities [Member]
Deposits	213,131,439	161,173,168
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents
Time deposits
Federal funds sold
Securities	753,321	1,358,121
Accrued interest receivable
Net loans	156,571,000	141,665,000
Loans held for sale
Mortgage servicing rights	328,360	285,927
Accrued interest payable
FHLB advances
Estimate of Fair Value Measurement [Member] \| Non-Interest Bearing Deposits [Member]
Deposits	10,285,561	10,325,832
Estimate of Fair Value Measurement [Member] \| Interest Bearing Deposits, Liabilities [Member]
Deposits	213,131,439	161,173,168
Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	4,469,007	7,135,719
Time deposits	250,000	250,000
Federal funds sold	54,351,000	1,604,000
Securities	44,902,860	48,343,028
Accrued interest receivable	800,249	775,641
Net loans	156,571,000	141,665,000
Loans held for sale	710,700
Mortgage servicing rights	328,360	285,927
Accrued interest payable	1,697	394
FHLB advances	$ 8,630,697	$ 2,139,117

Fair value portion of interest payable.

No definition available.

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Namespace Prefix:	ottw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of interest receivable.

+ References

No definition available.

+ Details

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Namespace Prefix:	ottw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of time deposit assets held by the entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	ottw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion 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. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

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

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of federal funds sold and securities borrowed or purchased under agreements to resell.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

+ Details

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

- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Glossary Loan
-URI http://asc.fasb.org/extlink&oid=6517073

+ Details

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

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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Balance Type:	debit
Period Type:	instant

- Details

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- Details

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- Details

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