Fair Value Measurements Fair Value of Financial Instrument Assumptions (Details) $ in Millions	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value of Financial Instrument Assumptions [Line Items]
Letters of Credit Potential Commitments, Amount	$ 51.2	$ 49.7
Second Amendment to Credit Facility [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 475.0
Basis Points Spread on Variable Rate - Credit Facility	250
Warehousing Agreement - First Amendment to Second Amended and Restated [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
M/I Financial Maximum Borrowing Capacity	$ 125.0
M/I Financial Temporary Increase Maximum Borrowing Capacity	150.0
Repurchase Agreement - Amendment No. 4 [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
M/I Financial Maximum Borrowing Capacity	35.0
M/I Financial Temporary Increase Maximum Borrowing Capacity	$ 50.0

Basis points added to the reference rate to compute the variable rate on the credit facility borrowings.

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- Definition

[Line Items] for Fair Value of Financial Instrument Assumptions [Table]

+ References

No definition available.

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- Definition

M/I Financial Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

M/I Financial Temporary Increase Maximum Borrowing Capacity

+ References

No definition available.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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