GOODWILL AND INTANGIBLE ASSETS: (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Goodwill
Goodwill at the beginning of year	$ 492,745				$ 492,745	$ 497,362
Impairment	0		$ 0
Impact email disposition (see note 4)					(5,684)
Allant purchase accounting adjustments					18
Change in foreign currency translation adjustment					(18)	(79)
Goodwill at the end of year		$ 492,745			592,731	492,745	$ 497,362
Accumulated impairment losses		120,100			120,100	120,100
Finite-Lived Intangible Assets, Net [Abstract]
Intangible assets gross		78,316			119,114	78,316	76,690
Accumulated amortization		(34,213)			(52,855)	(34,213)	(21,189)
Total		44,103			66,259	44,103	55,501
Intangible asset amortization					$ 18,600	15,500	11,400
Maximum
Goodwill
Amortization period					10 years
Minimum
Goodwill
Amortization period					2 years
Brazil reporting unit
Goodwill
Impairment						(502)
U.S. reporting unit
Goodwill
Goodwill at the end of year					$ 581,191
APAC reporting unit
Goodwill
Impairment						(5,413)
Goodwill at the end of year					11,540
Marketing Services and Audience Solutions
Goodwill
Goodwill at the beginning of year						497,362
Reallocation of segments						(496,860)
Goodwill at the end of year							497,362
Marketing Services and Audience Solutions | Brazil reporting unit
Goodwill
Impairment				$ (500)		(502)
Marketing Services and Audience Solutions | APAC reporting unit
Goodwill
Impairment		(5,400)
Marketing Services
Goodwill
Goodwill at the beginning of year	124,586				124,586
Reallocation of segments						124,627
Impact email disposition (see note 4)					(5,684)
Change in foreign currency translation adjustment					(12)	(41)
Goodwill at the end of year		124,586			118,890	124,586
Finite-Lived Intangible Assets, Net [Abstract]
Total					37
Marketing Services | U.S. reporting unit
Goodwill
Goodwill at the end of year					110,910
Marketing Services | APAC reporting unit
Goodwill
Goodwill at the end of year					7,980
Audience Solutions
Goodwill
Goodwill at the beginning of year	273,430				273,430
Reallocation of segments						277,516
Allant purchase accounting adjustments					18
Change in foreign currency translation adjustment						(50)
Goodwill at the end of year		273,430			273,448	273,430
Finite-Lived Intangible Assets, Net [Abstract]
Total					2,278
Audience Solutions | U.S. reporting unit
Goodwill
Goodwill at the end of year					273,448
Audience Solutions | APAC reporting unit
Goodwill
Impairment						(5,413)
Connectivity
Goodwill
Goodwill at the beginning of year	$ 94,729				94,729
Reallocation of segments						94,717
Change in foreign currency translation adjustment					(6)	12
Goodwill at the end of year		94,729			200,393	94,729
Finite-Lived Intangible Assets, Net [Abstract]
Total					63,944
Connectivity | U.S. reporting unit
Goodwill
Goodwill at the end of year					196,833
Connectivity | APAC reporting unit
Goodwill
Goodwill at the end of year					3,560
Developed technology.
Finite-Lived Intangible Assets, Net [Abstract]
Intangible assets gross		42,850			52,150	42,850	42,524
Accumulated amortization		(17,950)			(29,775)	(17,950)	(9,924)
Total		24,900			22,375	24,900	32,600
Developed technology. | Audience Solutions
Finite-Lived Intangible Assets, Net [Abstract]
Total					1,500
Developed technology. | Connectivity
Finite-Lived Intangible Assets, Net [Abstract]
Total					20,875
Customer/Trade name
Finite-Lived Intangible Assets, Net [Abstract]
Intangible assets gross		35,466			43,164	35,466	34,166
Accumulated amortization		(16,263)			(21,702)	(16,263)	(11,265)
Total		$ 19,203			21,462	19,203	$ 22,901
Customer/Trade name | Marketing Services
Finite-Lived Intangible Assets, Net [Abstract]
Total					37
Customer/Trade name | Audience Solutions
Finite-Lived Intangible Assets, Net [Abstract]
Total					778
Customer/Trade name | Connectivity
Finite-Lived Intangible Assets, Net [Abstract]
Total					20,647
Publisher relationship
Finite-Lived Intangible Assets, Net [Abstract]
Intangible assets gross					23,800
Accumulated amortization					(1,378)
Total					22,422
Publisher relationship | Connectivity
Finite-Lived Intangible Assets, Net [Abstract]
Total					22,422
Allant Television Division
Goodwill
Acquisition						1,377
Allant Television Division | Audience Solutions
Goodwill
Acquisition						$ 1,377
Arbor and Circulate
Goodwill
Acquisition					105,670
Arbor and Circulate | Connectivity
Goodwill
Acquisition					$ 105,670