Long-term Equity-based Compensation -Schedule of Share-based Compensation, Nonemployee Director Deferred Stock Unit Award Plan (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Share-based Compensation, Nonemployee Director Deferred Stock Unit Award Plan [Abstract]
Total fair value of DSUs that vested during the years	$ 0.9	$ 0.5	$ 0.1
Deferred Stock Units, Outstanding, Number, Period Start (in shares)	21,520
Deferred Stock Units, Granted and Vested in Period (in shares)	23,040
Deferred Stock Units, Outstanding, Number, Period End (in shares)	44,560	21,520
Deferred Stock Units, Outstanding, Weighted Average Exercise Price, Period Start (per share)	$ 32.68
Deferred Stock Units, Granted and Vested in Period, Weighted Average Exercise Price (per share)	38.20
Deferred Stock Units, Outstanding, Weighted Average Exercise Price, Period End (per share)	$ 35.54	$ 32.68