Restructuring and Exit Costs (Schedule of Restructuring and Exit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Costs incurred	$ (57)	$ 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	0	(300)	(855)
Accruals released	0		(142)
Restructuring liability as of March 31, 2018	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	(423)		(431)
Accruals released	(102)		(27)
Restructuring liability as of March 31, 2018	$ 337		$ 817