GOODWILL AND INTANGIBLE ASSETS: - Amounts allocated to intangible assets from acquisitions (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Developed technology, gross (Software)	$ 150,300	$ 113,600
Accumulated amortization	(93,560)	(85,008)
Total finite-lived intangible assets, net	56,740	28,592
Developed technology, gross (Software)
Finite-Lived Intangible Assets [Line Items]
Developed technology, gross (Software)	78,500	54,000
Accumulated amortization	(52,633)	(49,625)
Total finite-lived intangible assets, net	25,867	4,375
Trade name
Finite-Lived Intangible Assets [Line Items]
Developed technology, gross (Software)	41,000	35,800
Accumulated amortization	(29,251)	(26,128)
Total finite-lived intangible assets, net	11,749	9,672
Publisher Relationship
Finite-Lived Intangible Assets [Line Items]
Developed technology, gross (Software)	30,800	23,800
Accumulated amortization	(11,676)	(9,255)
Total finite-lived intangible assets, net	$ 19,124	$ 14,545
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period	2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period	6 years