Related Party Transactions (Affiliated Notes Receivable) (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 129,359	$ 132,571
U.S. Dollar floating rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 6,531	6,551
U.S. Dollar floating rate notes | Minimum
Related Party Transaction [Line Items]
Interest Rates	3.13%
U.S. Dollar floating rate notes | Maximum
Related Party Transaction [Line Items]
Interest Rates	3.74%
U.S. Dollar fixed rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 122,828	$ 126,020
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%