Business Combinations - Summary of Revenue and Earnings of Combined Entity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Supplementary pro forma information
Revenues		$ 470,566	$ 370,698
Income from operations		135,840	86,559
Walker & Dunlop net income		$ 82,347	$ 52,647
Diluted earnings per share		$ 2.65	$ 1.61
Weighted average diluted shares outstanding		31,024	32,737
Increase in tax expense		$ 100	$ 800
WDIS
Supplementary pro forma information
Total revenues	$ 2,600	9,300
Net income (loss) from operations	$ (500)	$ 1,900