Fair Value Measurements Fair Value of Financial Instrument Assumptions (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instrument Assumptions [Line Items]
Letters of Credit Potential Commitments, Amount	$ 33.9	$ 37.7
First Amendment to New Unsecured Credit Facility [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	400.0
Warehousing Agreement - Second Amended and Restated [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
M/I Financial Maximum Borrowing Capacity	125.0
Repurchase Agreement [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
M/I Financial Maximum Borrowing Capacity	$ 15.0	$ 35.0