Share-Based Compensation - Stock Options Unvested (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unvested Stock Options
Unvested stock options
Options outstanding at the beginning of the period (in shares)	57,000
Granted (in shares)	124,000
Vested (in shares)	(147,000)
Options outstanding at the end of the period (in shares)	34,000	57,000
Weighted-Average Grant-Date Fair Value
Options outstanding at the beginning of the period (in dollars per share)	$ 5.34
Granted (in dollars per share)	2.86
Vested (in dollars per share)	3.27
Options outstanding at the end of the period (in dollars per share)	$ 5.21	$ 5.34
Total future compensation cost related to unvested options that are expected to vest	$ 0.1
Weighted Average Period for Cost recognition	1 year
Key Officer Director and Managerial Employee Stock Options
Unvested stock options
Granted (in shares)	124,000	99,711
Weighted-Average Grant-Date Fair Value
Granted (in dollars per share)	$ 2.86	$ 3.52	$ 4.40
Total intrinsic value of stock options exercised	$ 5.1	$ 0.3	$ 0.8
Total fair value of option vested during the period	$ 0.5	$ 1.9	$ 1.9