Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Plans - 2013 Omnibus Equity Incentive Plan - Award Limitations - Additional Information (Detail)

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Stock-Based Compensation Plans - 2013 Omnibus Equity Incentive Plan - Award Limitations - Additional Information (Detail)
1 Months Ended 9 Months Ended
Aug. 31, 2016
shares
May 31, 2016
shares
Mar. 31, 2016
shares
Feb. 29, 2016
shares
Nov. 30, 2013
$ / shares
shares
Sep. 30, 2016
Incentive_Plan
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of active equity plans | Incentive_Plan           1
Common stock shares reserved for issuance of awards           5,500,000
Common stock shares available for grant           4,352,735
Increase of common stock share reserve approved           2,200,000
Share-based awards granted during the period 62,389 33,981 30,000 181,352   307,722
Description of awards granted under the 2013 Plan           In November 2013, MMI issued the following equity awards under the 2013 Plan (i) Deferred stock units ("DSUs") for an aggregate of 2,192,413 shares granted as replacement awards related to the prior SARs program to the MMREIS managing directors and (ii) DSUs for 83,334 shares granted to the Company's Co-chairman of the board of directors, William A. Millichap. The DSU's are fully vested and shares will be issued ratably over 5 years
Common stock sold and issued under IPO, price per share | $ / shares         $ 12.00  
Deferred stock units [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Fully vested deferred stock units settlement period         5 years  
Deferred stock units [Member] | MMREIS Managing Directors [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Fully vested deferred stock units         2,192,413  
Deferred stock units [Member] | Millichap [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Fully vested deferred stock units         83,334  
Restricted Stock Awards [Member] | Non-Employee Directors [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based awards granted during the period 0 14,742 0 0 30,000 14,742
Vesting period         3 years 3 years