Net Income Per Share - Schedule of Calculation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 0.4	$ (6.6)	$ 29.1	$ 25.4	$ 19.2	$ 28.0	$ 22.9	$ 72.6
Denominator – Weighted-average common shares outstanding (in thousands):
Basic	15,794,000			15,956,000			15,804,000	16,042,000
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares	71,000			169,000			100,000	193,000
Diluted	15,865,000			16,125,000			15,904,000	16,235,000
Net income per common share, Basic:	$ 0.02			$ 1.59			$ 1.45	$ 4.52
Net income per common share, Diluted:	$ 0.02			$ 1.57			$ 1.44	$ 4.47