Net Income (Loss) Per Share and Stockholders' Equity, Calculation of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income (loss)	$ 24.5	$ 14.9	$ 26.0	$ 26.3	$ 13.3	$ 22.1	$ 20.2	$ (292.2)	$ 91.7	$ (236.6)	$ 71.8
Denominator – Weighted-average common shares outstanding (in thousands):
Basic (in shares)									17,813	17,201	17,818
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares									220	0	179
Add: dilutive effect of warrants2									0	0	596
Diluted (in shares)									18,033	17,201	18,593
Net (loss) income per common share, Basic (in dollars per share)	$ 1.39	$ 0.84	$ 1.45	$ 1.47	$ 0.76	$ 1.29	$ 1.19	$ (16.85)	$ 5.15	$ (13.76)	$ 4.02
Net (loss) income per common share, Diluted (in dollars per share	$ 1.37	$ 0.82	$ 1.43	$ 1.44	$ 0.73	$ 1.21	$ 1.11	$ (16.85)	$ 5.09	$ (13.76)	$ 3.86