Fair-Value Measurements (Schedule of Fair Value of Financial Assets and Liabilities) (Details) - USD ($) $ in Thousands		Mar. 31, 2018		Dec. 31, 2017
Derivative asset:
Common stock of foreign public company, original cost		$ 500		$ 500
Interest Rate Current Swap [Member]
Derivative asset:
Liability for fixed rate leg		39,200		34,900
Receivable for floating rate leg		32,700		34,600
Quoted Prices in Active Markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents		14,806		13,601
Foreign currency options		75
Common stock of unaffiliated foreign public company	[1]	1,022		999
Liabilities:
Interest rate swaps
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents
Foreign currency options
Common stock of unaffiliated foreign public company
Liabilities:
Interest rate swaps		$ 6,554	[2]	$ 313	[3]

[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 $39.2 million receivable floating leg and $32.7 million liability fixed leg