Fair-Value Measurements (Schedule of Fair Value of Financial Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016
Derivative asset:
Common stock of foreign public company, original cost			$ 500
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	$ 13,601		8,468
Common stock of foreign public company	999	[1]	762
Interest rate swaps
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Cash equivalents
Common stock of foreign public company
Interest rate swaps	313	[2]	5,784	[3]
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Cash equivalents
Common stock of foreign public company
Interest rate swaps
Interest Rate Swap [Member]
Derivative liability:
Liability for fixed rate leg	34,900		21,400
Receivable for floating rate leg	$ 34,600		$ 15,600

[1] Original cost basis $0.5 million.

[2] Net of $34.9 million receivable floating leg and $34.6 million liability fixed leg

[3] Net of $21.4 million receivable floating leg and $15.6 million liability fixed leg