Net Income Per Share and Stockholders' Equity - Summary of Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
NET INCOME PER SHARE—BASIC:
Net income attributable to ADS	$ 28,670	$ 17,863	$ 60,950	$ 35,605
Dividends to redeemable convertible preferred stockholders	(478)	(470)	(975)	(959)
Dividends paid to unvested restricted stockholders	(15)	(16)	(30)	(35)
Net income available to common stockholders and participating securities	28,177	17,377	59,945	34,611
Undistributed income allocated to participating securities	(2,310)	(1,397)	(5,022)	(2,830)
Net income available to common stockholders – Basic	$ 25,867	$ 15,980	$ 54,923	$ 31,781
Weighted average number of common shares outstanding – Basic	56,929	55,269	56,776	55,286
Net income per common share – Basic	$ 0.45	$ 0.29	$ 0.97	$ 0.57
NET INCOME PER SHARE—DILUTED:
Net income available to common stockholders – Diluted	$ 25,867	$ 15,980	$ 54,923	$ 31,781
Weighted average number of common shares outstanding – Basic	56,929	55,269	56,776	55,286
Assumed exercise of stock options	629	624	598	667
Weighted average number of common shares outstanding – Diluted	57,558	55,893	57,374	55,953
Net income per common share – Diluted	$ 0.45	$ 0.29	$ 0.96	$ 0.57
Potentially dilutive securities excluded as anti-dilutive	6,303	6,211	6,229	6,349