Summary of Significant Accounting Policies - Investments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investment Amount	$ 62.1	$ 62.1
Colonial
Schedule of Equity Method Investments [Line Items]
Ownership	6.00%	6.00%
Investment Amount	$ 11.4	$ 11.4
Explorer
Schedule of Equity Method Investments [Line Items]
Ownership	12.62%	12.62%
Investment Amount	$ 48.6	$ 48.6
Cleopatra
Schedule of Equity Method Investments [Line Items]
Ownership	1.00%	1.00%
Investment Amount	$ 2.1	$ 2.1