Equity Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Millions	8 Months Ended	12 Months Ended
	Aug. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Equity Incentive Plan
Maximum number of common shares available for issuance (in shares)				6,100,000
Other Disclosures
Total fair value of shares vested	$ 1.1	$ 3.3
Amortization		$ 0.5	$ 0.8
Restricted share awards
Summary of non-vested shares/units
Unvested at the beginning of the period (in shares)	1,870,393	1,830,123	1,509,519
Granted (in shares)	1,398,705	1,207,926	1,116,394
Vested (in shares)	(2,241,683)	(771,508)	(793,540)
Forfeited (in shares)	(1,027,415)	(396,148)	(2,250)
Unvested at the end of the period (in shares)		1,870,393	1,830,123
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 6.21	$ 6.79	$ 5.70
Granted (in dollars per share)	5.53	6.24	8.14
Vested (in dollars per share)	6.52	7.72	6.61
Forfeited (in dollars per share)	$ 4.61	6.04	9.62
Unvested at the end of the period (in dollars per share)		$ 6.21	$ 6.79
Other Disclosures
Share-based compensation expense	$ (8.4)
2016 Performance Shares
Other Disclosures
Fair value assumptions, risk free interest rate		0.93%
Fair value assumptions, expected volatility rate		45.92%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		5.00%
2015 Performance Shares [Member]
Other Disclosures
Fair value assumptions, risk free interest rate			1.32%
Fair value assumptions, expected volatility rate			48.11%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate			4.00%
2017 Performance Shares
Other Disclosures
Fair value assumptions, risk free interest rate	1.51%
Fair value assumptions, expected volatility rate	43.92%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	6.00%
Predecessor | Restricted share awards
Other Disclosures
Share-based compensation expense	$ (2.7)	$ (5.0)	$ (5.1)