Debt MIF Warehousing Agreement (Details) $ in Thousands	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Maximum Borrowing Availability under all Credit Lines	$ 195,000	$ 200,000
Notes payable bank - financial service operations	104,026	$ 168,195
Warehousing Agreement - Second Amendment to Second Amended and Restated [Member]
Debt Instrument [Line Items]
M/I Financial Maximum Borrowing Capacity	125,000
M/I Financial Temporary Increase Maximum Borrowing Capacity	$ 160,000
LIBOR basis points	200.0
Repurchase Agreement - Amendment No. 4 [Member]
Debt Instrument [Line Items]
M/I Financial Maximum Borrowing Capacity	$ 35,000
M/I Financial Temporary Increase Maximum Borrowing Capacity	$ 50,000
Minimum [Member] | Repurchase Agreement - Amendment No. 4 [Member]
Debt Instrument [Line Items]
LIBOR basis points	250
Maximum [Member] | Repurchase Agreement - Amendment No. 4 [Member]
Debt Instrument [Line Items]
LIBOR basis points	212.5