Revision of Prior Period Financial Statements (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liabilities and stockholders' deficit
Deferred income taxes, net												$ 192.5	$ 192.9
Total liabilities												2,717.5	2,701.4
Accumulated deficit	$ (474.4)			$ (510.8)	$ (510.8)			$ (432.6)	$ (510.8)	$ (432.6)	$ (432.6)	(474.4)	(510.8)	$ (432.6)	$ (617.9)
Total stockholders' deficit												(245.9)	(281.8)	(136.6)	(676.0)
Total liabilities and stockholders' deficit												2,471.6	2,419.6
Revised Consolidated Statements of Operations
Income tax benefit									(1.5)	65.1	158.3
Net income (loss)	$ 6.9	$ 11.4	$ 9.7	$ 8.4	$ 17.1	$ 31.4	$ 25.4	$ (161.2)	$ 36.4	$ (87.3)	$ 185.3
Basic net income (loss) per share (in dollars per share)	$ 0.08	$ 0.14	$ 0.12	$ 0.10	$ 0.21	$ 0.39	$ 0.31	$ (1.91)	$ 0.45	$ (1.07)	$ 2.35
Diluted net income (loss) per share (in dollars per share)	$ 0.08	$ 0.14	$ 0.12	$ 0.10	$ 0.21	$ 0.38	$ 0.31	$ (1.91)	$ 0.45	$ (1.07)	$ 2.35
Revised Consolidated Statements of Comprehensive Income (Loss)
Net Income (Loss) Attributable to Parent	$ 6.9	$ 11.4	$ 9.7	$ 8.4	$ 17.1	$ 31.4	$ 25.4	$ (161.2)	$ 36.4	$ (87.3)	$ 185.3
Comprehensive income (loss)									27.4	(93.8)	185.3
Revised Statement of Stockholders' Deficit
Accumulated deficit, Balance at beginning of year				(510.8)				(432.6)	(510.8)	(432.6)	(617.9)
Net income (loss)	6.9	11.4	9.7	8.4	17.1	31.4	25.4	(161.2)	36.4	(87.3)	185.3
Accumulated deficit, Balance at end of year	$ (474.4)				(510.8)				(474.4)	(510.8)	(432.6)
Total stockholders' deficit												$ (245.9)	(281.8)	(136.6)	(676.0)
Revised Statement of Cash Flows
Net income (loss)									36.4	(87.3)	185.3
Deferred income taxes									4.3	(57.3)	(175.9)
Errors in accounting for deferred income taxes | As Reported
Liabilities and stockholders' deficit
Deferred income taxes, net													201.4
Total liabilities													2,709.9
Accumulated deficit				(519.3)	(519.3)			(437.8)	(519.3)	(437.8)	(437.8)		(519.3)	(437.8)	(622.0)
Total stockholders' deficit													(290.3)	(141.8)	(680.1)
Total liabilities and stockholders' deficit													2,419.6
Revised Consolidated Statements of Operations
Income tax benefit										61.8	157.2
Net income (loss)										$ (90.6)	$ 184.2
Basic net income (loss) per share (in dollars per share)										$ (1.11)	$ 2.34
Diluted net income (loss) per share (in dollars per share)										$ (1.11)	$ 2.34
Revised Consolidated Statements of Comprehensive Income (Loss)
Net Income (Loss) Attributable to Parent										$ (90.6)	$ 184.2
Comprehensive income (loss)										(97.1)	184.2
Revised Statement of Stockholders' Deficit
Accumulated deficit, Balance at beginning of year				(519.3)				(437.8)	(519.3)	(437.8)	(622.0)
Net income (loss)										(90.6)	184.2
Accumulated deficit, Balance at end of year					(519.3)					(519.3)	(437.8)
Total stockholders' deficit													(290.3)	(141.8)	(680.1)
Revised Statement of Cash Flows
Net income (loss)										(90.6)	184.2
Deferred income taxes										(54.0)	(174.8)
Errors in accounting for deferred income taxes | Adjustment
Liabilities and stockholders' deficit
Deferred income taxes, net													(8.5)
Total liabilities													(8.5)
Accumulated deficit				8.5	8.5			5.2	8.5	5.2	5.2		8.5	5.2	4.1
Total stockholders' deficit													8.5	5.2	4.1
Revised Consolidated Statements of Operations
Income tax benefit										3.3	1.1
Net income (loss)		0.2	0.3	0.2	0.8	0.9	0.8	0.8		3.3	1.1
Revised Consolidated Statements of Comprehensive Income (Loss)
Net Income (Loss) Attributable to Parent		0.2	0.3	0.2	0.8	0.9	0.8	0.8		3.3	1.1
Comprehensive income (loss)										3.3	1.1
Revised Statement of Stockholders' Deficit
Accumulated deficit, Balance at beginning of year				8.5				5.2	$ 8.5	5.2	4.1
Net income (loss)		$ 0.2	$ 0.3	$ 0.2	0.8	$ 0.9	$ 0.8	$ 0.8		3.3	1.1
Accumulated deficit, Balance at end of year					$ 8.5					8.5	5.2
Total stockholders' deficit													$ 8.5	$ 5.2	$ 4.1
Revised Statement of Cash Flows
Net income (loss)										3.3	1.1
Deferred income taxes										$ (3.3)	$ (1.1)