Annual report pursuant to Section 13 and 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)
$ / shares in Units, $ in Millions
 1 Months Ended 12 Months Ended
Nov. 30, 2015
shares
Aug. 31, 2015
shares
May. 31, 2015
shares
Feb. 28, 2015
shares
Dec. 31, 2014
shares
Nov. 30, 2014
shares
Aug. 31, 2014
shares
May. 31, 2014
shares
Feb. 28, 2014
shares
Nov. 30, 2013
$ / shares
shares
Dec. 31, 2015
USD ($)
Incentive_Plan
award
shares
Dec. 31, 2014
shares
Nov. 05, 2013
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share-based awards granted during the period 9,922 30,755 22,464 25,567 216,411 14,222 18,820 61,655 38,088   88,708 349,196  
IPO [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Vesting period                   3 years      
Common stock sold and issued under IPO, price per share | $ / shares                   $ 12.00     $ 12.00
Fully vested deferred stock units settlement period                   5 years      
2013 Omnibus Equity Incentive Plan [Member]                          
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                     3,477,730    
Common stock available for future issuance authorized annual percentage increase                     3.00%    
Increase of common stock share reserve approved                     1,100,000    
Description of awards granted under the 2013 Plan                     In November 2013, MMI issued the following equity awards under the 2013 Plan (i) 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 to be granted to the Company's Co-chairman of the board of directors, William A. Millichap ("Mr. Millichap"). The DSU's are fully vested and will be issued ratably over 5 years.    
Options & SARs [Member] | Minimum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted under the 2013 Plan                     500,000    
Options & SARs [Member] | Maximum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted increased under the 2013 Plan                     1,000,000    
Restricted Stock and RSUs [Member] | Minimum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted under the 2013 Plan                     500,000    
Restricted Stock and RSUs [Member] | Maximum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted increased under the 2013 Plan                     1,000,000    
Performance Shares [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Number of award limitation, performance units or performance shares | award                     1    
Performance Shares [Member] | Minimum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted under the 2013 Plan                     500,000    
Grant date fair value limitations to awards granted under the 2013 Plan | $                     $ 2    
Performance Shares [Member] | Maximum [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Share limitations to awards granted increased under the 2013 Plan                     1,000,000    
Grant date fair value limitations to awards granted under the 2013 Plan | $                     $ 5    
Deferred stock units [Member] | 2013 Omnibus Equity Incentive Plan [Member] | MMREIS Managing Directors [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Fully vested deferred stock units                   2,192,413 2,192,413    
Deferred stock units [Member] | 2013 Omnibus Equity Incentive Plan [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                   30,000      
Vesting period                   3 years      
Restricted Stock Awards [Member] | 2013 Omnibus Equity Incentive Plan [Member]                          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                          
Vesting period                     3 years