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	Non-controlling interest
Balance, beginning of period (shares) at Dec. 31, 2018				8,448,527	6,866,154
Balance, beginning of period at Dec. 31, 2018	$ 192.0			$ 0.1	$ 0.1		$ (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)				8,000
Shares withheld for taxes on equity transactions (in shares)				(2,254)
Net income attributable to controlling interest	3.6						2.0		2.0	1.6
Equity based compensation amortization	0.6							0.6	0.6
Balance, end of period (shares) at Mar. 31, 2019				8,454,273	6,866,154
Balance, end of period at Mar. 31, 2019	196.2			$ 0.1	$ 0.1		(7.9)	112.2	104.5	91.7
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)				152,633
Shares withheld for taxes on equity transactions (in shares)				(44,591)
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 attributable to controlling interest	2.8						1.5		1.5	1.3
Equity based compensation amortization	0.8							0.7	0.7	0.1
Shares withheld for taxes on equity transactions	(0.1)							(0.1)	(0.1)
Impact of transactions affecting non-controlling interest								(2.2)	(2.2)	2.2
Balance, end of period (shares) at Mar. 31, 2020		8,947,830	6,866,154	8,947,830	6,866,154	551,827
Balance, end of period at Mar. 31, 2020	$ 203.4			$ 0.1	$ 0.1	$ (3.8)	$ (6.6)	$ 120.2	$ 110.0	$ 93.4