Summary of Significant Accounting Policies - Narrative - Vessels, Deferred Revenues, Service Fees and Other (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Impaired Long-Lived Assets Held and Used [Line Items]
Operating Lease, Right-of-Use Asset	$ 23,832	$ 0		$ 32,052
Operating lease liability	29,491	0		$ 33,558
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		0
Unearned Premiums - Deferred revenue deficiency reserve	0	0
Service fee losses	0	$ 0	$ 0
Vessel related revenue
Impaired Long-Lived Assets Held and Used [Line Items]
Vessels, impairment	$ 0