Quarterly report pursuant to Section 13 or 15(d)

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

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Stock-Based Compensation Plans - 2013 Omnibus Equity Incentive Plan - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 6 Months Ended 12 Months Ended
Nov. 30, 2013
Jun. 30, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock awards and restricted stock units, vested shares   197,459  
Tax benefits from stock-based award activity included in cash flows from financing activities   $ 4,834  
Tax benefit from stock-based award activity included in additional paid-in capital   $ 524 $ 4,300
2013 Omnibus Equity Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of common stock shares withheld to pay employee statutory withholding taxes   21,814  
RSU vested, but not yet delivered   6,877  
Description of awards granted under the 2013 Plan   In November 2013, MMI issued the following deferred stock units ("DSUs") 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 granted to the Company's Co-chairman of the board of directors (Mr. Millichap). The DSU's are fully vested and shares will be issued 20% per year.  
2013 Omnibus Equity Incentive Plan [Member] | Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares issued under compensation plan   0  
Number of shares outstanding under compensation plan   0  
2013 Omnibus Equity Incentive Plan [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period for restricted stock awards and restricted stock units   3 years  
Restricted stock awards and restricted stock units, vested shares   197,459  
2013 Omnibus Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period for restricted stock awards and restricted stock units   5 years  
Restricted stock awards and restricted stock units, vested shares   197,459  
2013 Omnibus Equity Incentive Plan [Member] | SARs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares issued under compensation plan   0  
Number of shares outstanding under compensation plan   0  
2013 Omnibus Equity Incentive Plan [Member] | Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares issued under compensation plan   0  
Number of shares outstanding under compensation plan   0  
2013 Omnibus Equity Incentive Plan [Member] | Deferred stock units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
DSU's, percentage settled into actual stock 20.00%    
Fully vested deferred stock units remaining outstanding   1,820,596  
2013 Omnibus Equity Incentive Plan [Member] | 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    
2013 Omnibus Equity Incentive Plan [Member] | Deferred stock units [Member] | Millichap [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fully vested deferred stock units 83,334