Share-Based Compensation and Equity - Director Deferred Shares Activity (Details) - Director Deferred Shares [Member] - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-employee director deferred shares vested and outstanding	0.1
Aggregate intrinsic value of deferred shares released	$ 0.0	$ 0.2	$ 0.2
Total fair value of deferred shares vested		$ 0.2
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	12 months