Fair-Value Measurements (Schedule of Fair Value of Financial Assets and Liabilities) (Details) - USD ($) $ in Thousands		Jun. 30, 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		39,800		34,900
Receivable for floating rate leg		30,800		34,600
Quoted Prices in Active Markets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents		18,728		13,601
Foreign currency options		41
Common stock of unaffiliated foreign public company	[1]	962		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	[1]
Liabilities:
Interest rate swaps		$ 8,985	[2]	$ 313	[3]

[1] Original cost basis $0.5 million

[2] Net of $39.8 million receivable floating leg and $30.8 million liability fixed leg

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