Goodwill, Deferred Charges and Other Assets (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill, Gross			$ 5,814
Discounted cash flow projections period	9 years
Rate used to discount future cash flows for goodwill impairment test	8.30%
Finite Lived Intangible Assets Amortization Period Minimum		5 years
Other assets amortization period, maximum (in years)		15 years
Other Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization		$ 22,831	$ 20,766	$ 16,841