Related Party Transactions (Affiliated Notes Receivable) (Details) - Affiliated Entity - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 132,571	$ 137,636
U.S. Dollar floating rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 6,551	0
U.S. Dollar floating rate notes | Minimum
Related Party Transaction [Line Items]
Interest Rates	2.77%
U.S. Dollar floating rate notes | Maximum
Related Party Transaction [Line Items]
Interest Rates	3.12%
U.S. Dollar fixed rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 126,020	$ 137,636
U.S. Dollar fixed rate notes | Minimum
Related Party Transaction [Line Items]
Interest Rates	0.00%
U.S. Dollar fixed rate notes | Maximum
Related Party Transaction [Line Items]
Interest Rates	14.85%