Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock	Noncontrolling Interest
Beginning balance (deficit) (in shares) at Dec. 31, 2017		22,542,672
Beginning Balance (deficit) at Dec. 31, 2017	$ 313.1	$ 0.0	$ 254.6	$ (1.2)	$ 67.0	$ (7.5)	$ 0.2
Increase (Decrease) in Stockholders' Equity
Net income	15.9				15.3		0.6
Foreign currency translation	(0.4)			(0.4)
Issuance of restricted stock units (in shares)		45,963
Issuance of restricted stock units	0.0
Issuance of performance stock units (in shares)		48,174
Issuance of performance stock units	0.0
Non-cash stock-based compensation related to restricted stock units and performance share units	0.6		0.6
Distribution to noncontrolling interest	(0.8)						(0.8)
Ending balance (deficit) (in shares) at Mar. 31, 2018		22,636,809
Ending Balance (deficit) at Mar. 31, 2018	328.3	$ 0.0	255.2	(1.6)	82.2	(7.5)	0.0
Beginning balance (deficit) (in shares) at Dec. 31, 2017		22,542,672
Beginning Balance (deficit) at Dec. 31, 2017	313.1	$ 0.0	254.6	(1.2)	67.0	(7.5)	0.2
Increase (Decrease) in Stockholders' Equity
Net income	46.6
Ending balance (deficit) (in shares) at Sep. 30, 2018		22,729,564
Ending Balance (deficit) at Sep. 30, 2018	358.7	$ 0.0	256.7	(1.6)	111.1	(7.5)	0.0
Beginning balance (deficit) (in shares) at Mar. 31, 2018		22,636,809
Beginning Balance (deficit) at Mar. 31, 2018	328.3	$ 0.0	255.2	(1.6)	82.2	(7.5)	0.0
Increase (Decrease) in Stockholders' Equity
Net income	16.2				15.3		0.9
Foreign currency translation	(0.2)			(0.2)
Issuance of stock grants (in shares)		20,757
Issuance of stock grants	0.7		0.7
Non-cash stock-based compensation related to restricted stock units and performance share units	0.9		0.9
Distribution to noncontrolling interest	(0.8)						(0.8)
Ending balance (deficit) (in shares) at Jun. 30, 2018		22,657,566
Ending Balance (deficit) at Jun. 30, 2018	345.2	$ 0.0	256.8	(1.8)	97.6	(7.5)	0.1
Increase (Decrease) in Stockholders' Equity
Net income	14.5				13.5		1.0
Foreign currency translation	0.1			0.1
Issuance of restricted stock units (in shares)		71,998
Issuance of stock grants	0.0		0.0
Non-cash stock-based compensation related to restricted stock units and performance share units	(0.1)		(0.1)
Distribution to noncontrolling interest	(1.0)						(1.0)
Ending balance (deficit) (in shares) at Sep. 30, 2018		22,729,564
Ending Balance (deficit) at Sep. 30, 2018	$ 358.7	$ 0.0	256.7	(1.6)	111.1	(7.5)	0.0
Beginning balance (deficit) (in shares) at Dec. 31, 2018	22,783,976	22,783,976
Beginning Balance (deficit) at Dec. 31, 2018	$ 368.6	$ 0.0	257.7	(2.4)	120.7	(7.5)	0.1
Increase (Decrease) in Stockholders' Equity
Net income	10.9				10.6		0.3
Foreign currency translation	0.2			0.2
Issuance of restricted stock units (in shares)		7,518
Issuance of restricted stock units	0.0
Issuance of performance stock units (in shares)		62,094
Issuance of performance stock units	0.0
Non-cash stock-based compensation related to restricted stock units and performance share units	0.4		0.4
Treasury stock	(2.3)					(2.3)
Distribution to noncontrolling interest	(0.7)						(0.7)
Ending balance (deficit) (in shares) at Mar. 31, 2019		22,853,588
Ending Balance (deficit) at Mar. 31, 2019	$ 377.0	$ 0.0	258.0	(2.2)	131.3	(9.8)	(0.3)
Beginning balance (deficit) (in shares) at Dec. 31, 2018	22,783,976	22,783,976
Beginning Balance (deficit) at Dec. 31, 2018	$ 368.6	$ 0.0	257.7	(2.4)	120.7	(7.5)	0.1
Increase (Decrease) in Stockholders' Equity
Net income	42.2
Effective portion of unrealized loss on cash flow hedge	$ (0.9)
Ending balance (deficit) (in shares) at Sep. 30, 2019	22,948,766	22,948,766
Ending Balance (deficit) at Sep. 30, 2019	$ 378.3	$ 0.0	260.8	(3.3)	160.6	(39.8)	0.0
Beginning balance (deficit) (in shares) at Mar. 31, 2019		22,853,588
Beginning Balance (deficit) at Mar. 31, 2019	377.0	$ 0.0	258.0	(2.2)	131.3	(9.8)	(0.3)
Increase (Decrease) in Stockholders' Equity
Net income	16.3				15.2		1.1
Foreign currency translation	(0.1)			(0.1)
Effective portion of unrealized loss on cash flow hedge	(0.8)			(0.8)
Issuance of restricted stock units (in shares)		11,745
Issuance of restricted stock units	0.0
Issuance of stock grants (in shares)		14,076
Issuance of stock grants	0.5		0.5
Non-cash stock-based compensation related to restricted stock units and performance share units	1.0		1.0
Treasury stock	(11.3)					(11.3)
Distribution to noncontrolling interest	(0.7)						(0.7)
Ending balance (deficit) (in shares) at Jun. 30, 2019		22,879,409
Ending Balance (deficit) at Jun. 30, 2019	381.9	$ 0.0	259.5	(3.1)	146.5	(21.1)	0.1
Increase (Decrease) in Stockholders' Equity
Net income	15.0				14.2		0.8
Foreign currency translation	(0.1)			(0.1)
Effective portion of unrealized loss on cash flow hedge	(0.1)			(0.1)
Issuance of restricted stock units (in shares)		69,357
Issuance of restricted stock units	0.0
Non-cash stock-based compensation related to restricted stock units and performance share units	1.3		1.3
Treasury stock	(18.7)					(18.7)
Distribution to noncontrolling interest	$ (1.0)						(1.0)
Ending balance (deficit) (in shares) at Sep. 30, 2019	22,948,766	22,948,766
Ending Balance (deficit) at Sep. 30, 2019	$ 378.3	$ 0.0	$ 260.8	$ (3.3)	$ 160.6	$ (39.8)	$ 0.0