Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Service revenues	$ 1,623.0	$ 1,558.2	$ 1,507.6
Operating costs and expenses
Operating (exclusive of items shown separately below)	1,058.6	1,006.1	962.1
Selling, general and administrative	207.7	181.5	169.5
Depreciation and amortization	278.8	270.5	269.8
Acquisition and development costs	1.1	0.8	1.3
Loss (gain) on disposal of assets and asset impairments	1.7	(2.5)	11.4
Restructuring charges	0.6	0.1	3.4
Total operating costs and expenses	1,548.5	1,456.5	1,417.5
Operating income	74.5	101.7	90.1
Other (expense) income
Interest expense	(100.9)	(95.9)	(93.0)
Loss on debt extinguishments and modifications	0.0	(0.9)	(3.7)
Other (expense) income, net	(0.6)	9.1	3.7
Total other expense	(101.5)	(87.7)	(93.0)
(Loss) income before income taxes	(27.0)	14.0	(2.9)
Income tax (benefit) expense	(20.4)	4.6	(41.2)
Net income (loss)	$ (6.6)	$ 9.4	$ 38.3
Net (loss) income attributable to common stockholders per share
Basic (loss) income per share (in dollars per share)	$ (0.07)	$ 0.11	$ 0.43
Diluted (loss) income per share (in dollars per share)	$ (0.07)	$ 0.11	$ 0.43
Basic average shares outstanding (in shares)	89,022,531	88,590,491	88,323,213
Diluted average shares outstanding (in shares)	89,022,531	89,446,917	88,887,812