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
Balance as of December 31, 2018 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
Balance as of March 31, 2019 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, 2018	22,783,976	22,783,976
Balance as of December 31, 2018 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	22,853,588
Balance as of March 31, 2019 at Mar. 31, 2019	$ 377.0	$ 0.0	$ 258.0	$ (2.2)	$ 131.3	$ (9.8)	$ (0.3)