Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State and Local Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current expense: State									$ 0.7	$ 0.4	$ 0.4
Total									0.7	0.4	0.4
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred provision: State									0.3	0.2	0.1
Total									0.3	0.2	0.1
Income taxes	$ 0.1	$ 0.3	$ 0.4	$ 0.2	$ 0.2	$ 0.0	$ 0.2	$ 0.2	1.0	0.6	0.5
Summary of the Provision for Income Taxes [Line Items]
Deferred Tax Assets, Net	$ 0.0				$ 0.0				0.0	0.0
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount									$ 0.0	$ 0.0	$ 0.0
Earliest Tax Year
Summary of the Provision for Income Taxes [Line Items]
Open Tax Year									2014
Latest Tax Year
Summary of the Provision for Income Taxes [Line Items]
Open Tax Year									2017