SUMMARY OF ACCOUNTING POLICIES - Intangible Assets (Details) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Components of acquired intangible assets
Intangible assets residual value	$ 0
Gross Carrying Amount	610,950,000	$ 544,601,000
Accumulated Amortization	(186,517,000)	(182,420,000)
Net Carrying Amount	424,433,000	362,181,000
Intangible assets fully amortized and removed	38,300,000
Total intangible asset amortization expense	78,640,000	81,396,000	$ 65,965,000
Estimated future annual amortization expense for acquired intangible assets
2019	75,319,000
2020	68,981,000
2021	64,440,000
2022	55,301,000
2023	46,762,000
Thereafter	113,630,000
Net Carrying Amount	424,433,000	362,181,000
Customer-related intangibles
Components of acquired intangible assets
Gross Carrying Amount	306,943,000	260,704,000
Accumulated Amortization	(79,051,000)	(105,912,000)
Net Carrying Amount	227,892,000	154,792,000
Estimated future annual amortization expense for acquired intangible assets
Net Carrying Amount	$ 227,892,000	154,792,000
Customer-related intangibles | Maximum
Components of acquired intangible assets
Useful life	10 years
Customer-related intangibles | Weighted-average
Components of acquired intangible assets
Useful life	7 years 1 month 6 days
Licenses and other intangibles
Components of acquired intangible assets
Gross Carrying Amount	$ 304,007,000	283,897,000
Accumulated Amortization	(107,466,000)	(76,508,000)
Net Carrying Amount	196,541,000	207,389,000
Estimated future annual amortization expense for acquired intangible assets
Net Carrying Amount	$ 196,541,000	$ 207,389,000
Licenses and other intangibles | Weighted-average
Components of acquired intangible assets
Useful life	6 years 1 month 6 days