Debt (Bank Of America Credit Facility) (Narrative) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
	Mar. 03, 2016	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Contractual facility		$ 270,746	$ 271,732
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