Borrowings (Bank Of America Credit Facility) (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
	Mar. 03, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Contractual facility		$ 271,732	$ 266,134
US Bank Of America Credit Facility [Member]
Debt Instrument [Line Items]
Contractual facility	$ 55,000	$ 55,000	$ 55,000
Reduced leverage ratio	0.25%
Earliest period subjected to repayment of borrowings		18 months