UNAUDITED INTERIM CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Treasury Stock	Accumulated deficit	Additional paid-in capital	Total controlling interest shareholders’ equity	Noncontrolling interest
Balance, beginning of period (shares) at Dec. 31, 2018				8,448,527	6,866,154	0
Balance, beginning of period at Dec. 31, 2018	$ 192.0			$ 0.1	$ 0.1	$ 0.0	$ (9.9)	$ 111.6	$ 101.9	$ 90.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under share-based compensation plans (in shares)				214,780
Shares withheld for taxes on equity transactions (in shares)				(41,202)
Shares withheld for taxes on equity transactions	(0.3)							(0.3)	(0.3)
Issuance of Class A Common Stock to related party (in shares)				206,897
Issuance of Class A Common Stock to related party	3.0							3.0	3.0
Repurchase of Class A Common Stock (in shares)						(47,474)
Repurchase of Class A Common Stock	(0.3)					$ (0.3)			(0.3)
Net income (loss) attributable to controlling interest	4.5						2.5		2.5	2.0
Equity based compensation amortization	2.4							2.2	2.2	0.2
Benefit from reversal of valuation allowance	1.2							1.2	1.2
Impact of transactions affecting noncontrolling interest								3.8	3.8	(3.8)
Balance, end of period (shares) at Sep. 30, 2019				8,829,002	6,866,154	47,474
Balance, end of period at Sep. 30, 2019	202.5			$ 0.1	$ 0.1	$ (0.3)	(7.4)	121.5	114.0	88.5
Balance, beginning of period (shares) at Jun. 30, 2019				8,717,026	6,866,154	0
Balance, beginning of period at Jun. 30, 2019	202.1			$ 0.1	$ 0.1	$ 0.0	(6.9)	119.9	113.2	88.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under share-based compensation plans (in shares)				113,159
Shares withheld for taxes on equity transactions (in shares)				(1,183)
Shares withheld for taxes on equity transactions	0.1							0.1	0.1
Repurchase of Class A Common Stock (in shares)						(47,474)
Repurchase of Class A Common Stock	(0.3)					$ (0.3)			(0.3)
Net income (loss) attributable to controlling interest	(0.9)						(0.5)		(0.5)	(0.4)
Equity based compensation amortization	0.9							0.8	0.8	0.1
Benefit from reversal of valuation allowance	0.6							0.6	0.6
Impact of transactions affecting noncontrolling interest								0.1	0.1	(0.1)
Balance, end of period (shares) at Sep. 30, 2019				8,829,002	6,866,154	47,474
Balance, end of period at Sep. 30, 2019	202.5			$ 0.1	$ 0.1	$ (0.3)	(7.4)	121.5	114.0	88.5
Balance, beginning of period (shares) at Dec. 31, 2019		8,839,788	6,866,154	8,839,788	6,866,154	113,937
Balance, beginning of period at Dec. 31, 2019	203.0			$ 0.1	$ 0.1	$ (0.7)	(8.1)	121.8	113.2	89.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under share-based compensation plans (in shares)				322,110
Shares withheld for taxes on equity transactions (in shares)				(81,309)
Shares withheld for taxes on equity transactions	(0.3)							(0.3)	(0.3)
Repurchase of Class A Common Stock (in shares)		(344,827)				(437,890)
Repurchase of Class A Common Stock	(3.1)	$ (2.4)				$ (3.1)			(3.1)
Net income (loss) attributable to controlling interest	(11.8)						(6.6)		(6.6)	(5.2)
Equity based compensation amortization	2.8							2.7	2.7	0.1
Impact of transactions affecting noncontrolling interest								(2.2)	(2.2)	2.2
Balance, end of period (shares) at Sep. 30, 2020		9,080,589	6,866,154	9,080,589	6,866,154	551,827
Balance, end of period at Sep. 30, 2020	190.6			$ 0.1	$ 0.1	$ (3.8)	(14.7)	122.0	103.7	86.9
Balance, beginning of period (shares) at Jun. 30, 2020				9,031,495	6,866,154	551,827
Balance, beginning of period at Jun. 30, 2020	195.2			$ 0.1	$ 0.1	$ (3.8)	(11.5)	121.0	105.9	89.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under share-based compensation plans (in shares)				51,975
Shares withheld for taxes on equity transactions (in shares)				(2,881)
Net income (loss) attributable to controlling interest	(5.7)						(3.2)		(3.2)	(2.5)
Equity based compensation amortization	1.1							1.1	1.1
Impact of transactions affecting noncontrolling interest								(0.1)	(0.1)	0.1
Balance, end of period (shares) at Sep. 30, 2020		9,080,589	6,866,154	9,080,589	6,866,154	551,827
Balance, end of period at Sep. 30, 2020	$ 190.6			$ 0.1	$ 0.1	$ (3.8)	$ (14.7)	$ 122.0	$ 103.7	$ 86.9