Nature of Business and Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred financing costs:
Accumulated amortization of deferred financing costs	$ 1.8	$ 1.5
Deferred financing costs, net	1.5	1.8
Interest expense
Deferred financing costs:
Amortization of deferred financing costs	$ 0.3	$ 0.5	$ 0.5
Customer relationships, non-compete agreement and affiliate agreements | Minimum
Goodwill and other intangibles:
useful lives	1 year
Customer relationships, non-compete agreement and affiliate agreements | Maximum
Goodwill and other intangibles:
useful lives	10 years