Restructuring and Exit Costs (Schedule of Restructuring and Exit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Costs incurred	$ 78	$ 0	$ 21	$ 997
February 2017 Restructuring Plan | Employee Severance Costs
Restructuring Reserve [Roll Forward]
Restructuring liability as of December 31, 2017			0	0	$ 0
Costs incurred			0		997
Amounts paid		$ (300)	0	(600)	(855)
Accruals released			0		(142)
Restructuring liability as of June 30, 2018	0		0		0
September 2017 Restructuring Plan | Employee Severance Costs
Restructuring Reserve [Roll Forward]
Restructuring liability as of December 31, 2017			817	$ 0	0
Costs incurred			45		1,275
Amounts paid			(689)		(431)
Accruals released			(110)		(27)
Restructuring liability as of June 30, 2018	$ 63		$ 63		$ 817