Debt - Adjusted Financial Statements to Apply Adopted Guidance (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021		Dec. 31, 2020		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019		Jun. 15, 2021	Dec. 31, 2018
Statement of operations
Total before tax													$ 23.9		$ (22.0)	[1]	$ 57.8
Income tax expense/(benefit)		$ 9.5	$ 15.4	$ (2.5)	$ 0.9		$ (0.3)		$ (3.1)	$ (2.0)	$ (0.3)		23.3		(5.7)	[1]	7.6
Net income/(loss)		7.5	$ (12.6)	$ 6.5	(0.8)		(3.7)		$ (10.5)	$ (0.2)	(1.9)		0.6		(16.3)	[2]	50.2
Adjustments to reconcile net (loss)/income to cash provided by operating activities:
Deferred income taxes													12.5		(6.3)	[3]	(0.9)
Deferred financing fee amortization													0.3		0.7	[3]	0.0
Cash provided by operating activities													26.4		6.3	[3]	58.1
Net increase in cash and cash equivalents													101.4		(5.2)	[3]	(11.5)
Cash and cash equivalents, beginning of period					$ 11.6	[3]					$ 16.8	[3]	11.6	[3]	16.8	[3]	28.3
Cash and cash equivalents, end of period		$ 113.0					$ 11.6	[3]					113.0		$ 11.6	[3]	$ 16.8	[3]
Net income per weighted average share - basic (in dollars per share)		$ 0.05	$ (80,000.00)	$ 40,000.00	$ (10,000.00)		$ (30,000.00)		$ (70,000.00)	$ 0	$ (10,000.00)				$ (0.11)	[1]	$ 0.34
Net income per weighted average share - diluted (in dollars per share)		$ 0.04	$ (80,000.00)	$ 30,000.00	$ (10,000.00)		$ (30,000.00)		$ (70,000.00)	$ 0	$ (10,000.00)				$ (0.11)	[1]	0.34
Balance Sheet
Deferred income taxes		$ 12.7					$ 5.6	[4]					12.7		$ 5.6	[4]
Long-term debt		240.4					274.6	[4]					240.4		274.6	[4]
Total current and long-term liabilities		$ 407.1					$ 400.6	[4]					$ 407.1		$ 400.6	[4]
Common stock, par value (in dollars per share)		$ 0.001					$ 0.001						$ 0.001		$ 0.001		$ 0.001		$ 0.001
Common stock; $0.001 par value; 2 billion shares authorized; 161,791,602 and 146,461,249 shares issued; 161,689,984 and 146,361,981 outstanding at December 31, 2021 and 2020, respectively	[4]						$ 0.1								$ 0.1
Capital in excess of par value of common stock	[4]						520.9								520.9
Retained earnings	[4]						60.3								60.3
Accumulated other comprehensive loss	[4]						(44.4)								(44.4)
Treasury stock, common; 101,131 and 99,268 shares at September 30, 2021 and December 31, 2020, respectively	[4]						(0.7)								(0.7)
Total equity		$ 795.4					536.2	[4]					$ 795.4		536.2	[4]	$ 544.0			$ 489.6
Total liabilities and equity		1,202.5					936.8	[4]					1,202.5		936.8	[4]
Statement of cash flows
Net (loss)/income		7.5	$ (12.6)	$ 6.5	$ (0.8)		(3.7)		$ (10.5)	$ (0.2)	$ (1.9)		0.6		(16.3)	[2]	50.2
Accounting Standards Update 2020-06
Statement of operations
Interest expense, net													0.3		0.3
Total before tax													23.9		(22.0)
Income tax expense/(benefit)													23.3		(5.7)
Net income/(loss)													0.6		(16.3)
Adjustments to reconcile net (loss)/income to cash provided by operating activities:
Deferred income taxes													12.5		(6.3)
Deferred financing fee amortization													0.3		0.7
Cash provided by operating activities													$ 13.4		$ (21.9)
Net income per weighted average share - basic (in dollars per share)													$ 0		$ (0.11)
Net income per weighted average share - diluted (in dollars per share)													$ 0		$ (0.11)
Balance Sheet
Deferred income taxes		12.7					5.6						$ 12.7		$ 5.6
Long-term debt							274.6								274.6
Total current and long-term liabilities		253.1					280.2						253.1		280.2
Common stock; $0.001 par value; 2 billion shares authorized; 161,791,602 and 146,461,249 shares issued; 161,689,984 and 146,361,981 outstanding at December 31, 2021 and 2020, respectively		0.1					0.1						0.1		0.1
Capital in excess of par value of common stock		778.1					520.9						778.1		520.9
Retained earnings		60.9					60.3						60.9		60.3
Accumulated other comprehensive loss		(42.9)					(44.4)						(42.9)		(44.4)
Treasury stock, common; 101,131 and 99,268 shares at September 30, 2021 and December 31, 2020, respectively		(0.8)					(0.7)						(0.8)		(0.7)
Total equity		795.4					536.2						795.4		536.2
Total liabilities and equity		1,048.5					816.4						1,048.5		816.4
Statement of cash flows
Net (loss)/income													0.6		(16.3)
As computed under ASC 470-20
Statement of operations
Interest expense, net													7.3		3.7
Total before tax													16.9		(25.4)
Income tax expense/(benefit)													21.7		(6.5)
Net income/(loss)													(4.8)		(18.9)
Adjustments to reconcile net (loss)/income to cash provided by operating activities:
Deferred income taxes													10.9		(7.1)
Deferred financing fee amortization													7.3		4.1
Cash provided by operating activities													13.4		(21.9)
Net increase in cash and cash equivalents													101.4		(5.2)
Cash and cash equivalents, beginning of period					11.6						16.8		11.6		16.8
Cash and cash equivalents, end of period		113.0					11.6						$ 113.0		$ 11.6		16.8
Net income per weighted average share - basic (in dollars per share)													$ (0.03)		$ (0.13)
Net income per weighted average share - diluted (in dollars per share)													$ (0.03)		$ (0.13)
Balance Sheet
Deferred income taxes		19.3					13.9						$ 19.3		$ 13.9
Long-term debt		209.6					236.7						209.6		236.7
Total current and long-term liabilities		228.9					250.6						228.9		250.6
Common stock; $0.001 par value; 2 billion shares authorized; 161,791,602 and 146,461,249 shares issued; 161,689,984 and 146,361,981 outstanding at December 31, 2021 and 2020, respectively		0.1					0.1						0.1		0.1
Capital in excess of par value of common stock		810.3					553.1						810.3		553.1
Retained earnings		52.9					57.7						52.9		57.7
Accumulated other comprehensive loss		(42.9)					(44.4)						(42.9)		(44.4)
Treasury stock, common; 101,131 and 99,268 shares at September 30, 2021 and December 31, 2020, respectively		(0.8)					(0.7)						(0.8)		(0.7)
Total equity		819.6					565.8						819.6		565.8
Total liabilities and equity		1,048.5					816.4						1,048.5		816.4
Statement of cash flows
Net (loss)/income													(4.8)		(18.9)
Effect of change | Accounting Standards Update 2020-06
Statement of operations
Interest expense, net													(7.0)		(3.4)
Total before tax													7.0		3.4
Income tax expense/(benefit)													1.6		0.8
Net income/(loss)													5.4		2.6
Adjustments to reconcile net (loss)/income to cash provided by operating activities:
Deferred income taxes													1.6		0.8
Deferred financing fee amortization													(7.0)		(3.4)
Cash provided by operating activities													0.0		0.0
Net increase in cash and cash equivalents													0.0		0.0
Cash and cash equivalents, beginning of period					$ 0.0						$ 0.0		0.0		0.0
Cash and cash equivalents, end of period		0.0					0.0						$ 0.0		$ 0.0		$ 0.0
Net income per weighted average share - basic (in dollars per share)													$ 0.03		$ 0.02
Net income per weighted average share - diluted (in dollars per share)													$ 0.03		$ 0.02
Balance Sheet
Deferred income taxes		(6.6)					(8.3)						$ (6.6)		$ (8.3)
Long-term debt		30.8					37.9						30.8		37.9
Total current and long-term liabilities		24.2					29.6						24.2		29.6
Common stock; $0.001 par value; 2 billion shares authorized; 161,791,602 and 146,461,249 shares issued; 161,689,984 and 146,361,981 outstanding at December 31, 2021 and 2020, respectively		0.0					0.0						0.0		0.0
Capital in excess of par value of common stock		(32.2)					(32.2)						(32.2)		(32.2)
Retained earnings		8.0					2.6						8.0		2.6
Accumulated other comprehensive loss		0.0					0.0						0.0		0.0
Treasury stock, common; 101,131 and 99,268 shares at September 30, 2021 and December 31, 2020, respectively		0.0					0.0						0.0		0.0
Total equity		(24.2)					(29.6)						(24.2)		(29.6)
Total liabilities and equity		$ 0.0					$ 0.0						0.0		0.0
Statement of cash flows
Net (loss)/income													$ 5.4		$ 2.6

[1] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.

[2] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.

[3] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.

[4] As adjusted for the adoption of ASU 2020-06 using the full retrospective method.