Fair-Value Measurements (Reconciliation of Changes in Derivatives Classified as Level 3) (Details) - Fair Value, Inputs, Level 3 [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	$ 0
Initial valuation of Preferred Distribution Rate Reset Election	(34,450)
Net Loss for the period included in earnings	(10,472)
Allocation of Distribution Paid-in-kind	(287)
Ending Balance	$ (45,209)