Earnings per Share - Schedule of Earnings Per Share - Basic and Diluted (Details) - Common Class A - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Net income attributable to HLI
Basic EPS of Class A common stock	$ 8,845	$ 5,464
Assumed exercise and vesting of employee awards	119	83
Diluted EPS of Class A common stock	$ 8,964	$ 5,547
Weighted-Average Shares
Weighted-average basic EPS of Class A common stock (in shares)	22,248,547	17,981,601
Weighted-average assumed vesting of employee awards (in shares)	524,940	477,814
Weighted-average diluted EPS of Class A common stock (in shares)	22,773,487	18,459,415
Per share amount
Basic EPS of Class A common stock (in dollars per share)	$ 0.40	$ 0.30
Diluted EPS of Class A common stock (in dollars per share)	$ 0.39	$ 0.30