GOODWILL AND INTANGIBLE ASSETS: - Amounts allocated to intangible assets from acquisitions (Details) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 113,600	$ 113,600
Accumulated amortization	(78,685)	(69,072)
Total finite-lived intangible assets, net	34,915	44,528
Developed technology, gross (Software)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	54,000	54,000
Accumulated amortization	(48,054)	(43,383)
Total finite-lived intangible assets, net	5,946	10,617
Trade name
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	35,800	35,800
Accumulated amortization	(23,359)	(20,400)
Total finite-lived intangible assets, net	12,441	15,400
Publisher Relationship
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	23,800	23,800
Accumulated amortization	(7,272)	(5,289)
Total finite-lived intangible assets, net	$ 16,528	$ 18,511
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period	2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period	6 years