Related Party Transactions (Affiliated Notes Receivable) (Details) - Affiliated Entity - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 37,861	$ 38,145
U.S. Dollar floating rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 34,085	34,268
U.S. Dollar floating rate notes | Minimum
Related Party Transaction [Line Items]
Interest Rates	3.73%
U.S. Dollar floating rate notes | Maximum
Related Party Transaction [Line Items]
Interest Rates	3.80%
U.S. Dollar fixed rate notes
Related Party Transaction [Line Items]
Total long-term notes receivable - affiliated	$ 3,776	$ 3,877
U.S. Dollar fixed rate notes | Minimum
Related Party Transaction [Line Items]
Interest Rates	8.15%
U.S. Dollar fixed rate notes | Maximum
Related Party Transaction [Line Items]
Interest Rates	14.85%