SEGMENT INFORMATION: (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Revenues:
Total segment revenues	$ 244,781	$ 234,871	$ 225,240	$ 212,514	$ 224,867	$ 223,312	$ 217,267	$ 214,801	$ 917,406	$ 880,247	$ 850,088
Gross profit:
Total segment gross profit	123,297	118,951	110,168	98,554	106,573	106,844	97,162	91,982	450,970	402,561	361,706
Income (loss) from operations:
Income (loss) from operations	$ 4,795	$ 11,058	$ 453	$ (5,707)	$ (8,709)	$ 9,115	$ 7,120	$ 8,162	10,599	15,689	(13,063)
Gains, losses and other items, net									6,373	8,373	12,132
Depreciation and amortization:
Depreciation and amortization									86,371	82,690	85,463
Operating segment
Revenues:
Total segment revenues									917,406	880,247	850,088
Gross profit:
Total segment gross profit									482,305	427,084	381,172
Income (loss) from operations:
Income (loss) from operations									225,895	209,193	180,671
Depreciation and amortization:
Total depreciation and amortization									48,210	42,741	42,829
Operating segment | Marketing Services
Revenues:
Total segment revenues									379,047	410,840	449,772
Gross profit:
Total segment gross profit									139,185	140,647	152,258
Income (loss) from operations:
Income (loss) from operations									83,304	80,622	74,371
Depreciation and amortization:
Depreciation and amortization									6,885	7,549	9,988
Operating segment | Audience Solutions
Revenues:
Total segment revenues									327,358	322,065	297,846
Gross profit:
Total segment gross profit									202,235	198,186	167,715
Income (loss) from operations:
Income (loss) from operations									124,192	123,238	109,598
Depreciation and amortization:
Depreciation and amortization									12,553	13,286	12,909
Operating segment | Connectivity
Revenues:
Total segment revenues									211,001	147,342	102,470
Gross profit:
Total segment gross profit									140,885	88,251	61,199
Income (loss) from operations:
Income (loss) from operations									18,399	5,333	(3,298)
Depreciation and amortization:
Depreciation and amortization									28,772	21,906	19,932
Reconciling items
Gross profit:
Purchased intangible asset amortization									23,920	18,644	15,466
Non-cash stock compensation									6,416	5,879	2,150
Accelerated amortization									999	0	1,850
Income (loss) from operations:
Corporate expenses (principally general and administrative)									120,770	117,342	125,994
Gains, losses and other items, net									6,373	8,373	12,132
Impairment of goodwill and other									0	0	6,829
Purchased intangible asset amortization									23,920	18,644	15,466
Non-cash stock compensation									63,234	49,145	31,463
Accelerated amortization									$ 999	$ 0	$ 1,850