BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Recently Issued Accounting Pronouncements) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Recently Issued Accounting Pronouncements
Revenues	$ 657.6	$ 649.4	$ 653.5	$ 643.5	$ 638.0	$ 550.2	$ 506.7	$ 504.9	$ 2,604.0	$ 2,199.8	$ 1,721.7
Operating costs (excluding depreciation and amortization and including stock-based compensation—Note 11)	239.3	234.9	232.0	235.7	234.2	195.0	179.9	173.8	941.9	782.9	578.7
Selling, general and administrative expenses (including stock-based compensation)	121.9	118.0	121.6	128.3	117.1	108.8	104.7	105.6	489.8	436.2	386.4
Depreciation And Amortization	176.2	191.2	195.9	184.1	181.3	155.7	131.4	138.5	747.4	606.9	516.3
Provision for income taxes	(23.1)	20.9	22.9	5.4	11.0	0.6	0.2	6.6	26.1	18.4	8.5
Net income	43.8	23.4	11.5	23.2	23.2	$ 27.0	$ 19.8	$ 15.7	101.9	85.7	$ (76.2)
Assets
Other current assets	22.6				34.0				22.6	34.0
Property and equipment, net	5,447.2				5,016.0				5,447.2	5,016.0
Other assets	170.0				141.7				170.0	141.7
Liabilities
Deferred revenue, current	164.4				146.0				164.4	146.0
Deferred revenue, non-current	1,096.8				989.7				1,096.8	989.7
Deferred income taxes, net	143.2				40.2				143.2	40.2
Stockholders' equity
Accumulated deficit	(377.2)				$ (479.1)				(377.2)	(479.1)
As Reported
Assets
Other current assets	22.6								22.6
Property and equipment, net	5,447.2								5,447.2
Other assets	170.0								170.0
Liabilities
Deferred revenue, current	164.4								164.4
Deferred revenue, non-current	1,096.8								1,096.8
Deferred income taxes, net	143.2								143.2
Stockholders' equity
Accumulated deficit	(377.2)								(377.2)
As Adjusted | Accounting Standards Update 2014-09 [Member]
Assets
Other current assets	29.7								29.7
Property and equipment, net	5,427.6								5,427.6
Other assets	175.6								175.6
Liabilities
Deferred revenue, current	162.9								162.9
Deferred revenue, non-current	1,076.3								1,076.3
Deferred income taxes, net	147.1								147.1
Stockholders' equity
Accumulated deficit	(366.0)								(366.0)
Pro Forma [Member] | Accounting Standards Update 2014-09 [Member]
Recently Issued Accounting Pronouncements
Revenues	(0.3)	(0.4)	(0.4)	(0.4)					(1.5)	20.5
Operating costs (excluding depreciation and amortization and including stock-based compensation—Note 11)										18.8
Selling, general and administrative expenses (including stock-based compensation)	1.0	(0.3)	0.6	(0.2)					1.1	0.2
Depreciation And Amortization	(0.1)	(0.2)	(0.3)	(0.3)					(0.9)	(0.7)
Provision for income taxes	(0.2)		(2.5)						(2.7)	0.8
Net income	(1.0)	$ 0.1	$ 1.8	$ 0.1					1.0	$ 1.4
Effect of Adoption | Accounting Standards Update 2014-09 [Member]
Assets
Other current assets	7.1								7.1
Property and equipment, net	(19.6)								(19.6)
Other assets	5.6								5.6
Liabilities
Deferred revenue, current	(1.5)								(1.5)
Deferred revenue, non-current	(20.5)								(20.5)
Deferred income taxes, net	3.9								3.9
Stockholders' equity
Accumulated deficit	$ 11.2								$ 11.2