STOCK-BASED COMPENSATION - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Stock Option Rollforward
Stock options outstanding at the beginning of the period (in shares)	3,114	3,998
Options granted (in shares)	0	195
Options exercised (in shares)	(287)	(574)
Options canceled and forfeited (in shares)	(39)	(97)
Options outstanding at the end of the period (in shares)	2,788	3,522
Weighted-average fair value of grants during the period (in dollars per share)	$ 0	$ 8.47
Total intrinsic value of options exercised during the period	$ 3,726	$ 8,525
Weighted-average remaining recognition period at period-end (in years)	2 years 3 months 25 days	2 years 6 months 7 days
Stock Award Rollforward
Stock awards outstanding at the beginning of the period (in shares)	7,820	5,939
Stock awards granted (in shares)	5,123	2,112
Stock awards vested (in shares)	(1,945)	(1,720)
Stock awards canceled and forfeited (in shares)	(663)	(433)
Stock awards outstanding at the end of the period: (in shares)	10,335	5,898
Weighted-average fair value of grants during the period (in dollars per share)	$ 22.35	$ 22.01
Weighted-average remaining recognition period at period-end (in years)	2 years 3 months 10 days	2 years 5 months 8 days
Total unrecognized compensation expense at period-end	$ 129,136	$ 79,121