Restructuring and Exit Costs (Summary of Restructuring Liability by Plan) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Costs incurred	$ 1,300	$ 1,000	$ 2,282	$ 297	$ 2,512
February 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring liability		0	0
Costs incurred			997
Restructuring cash payments			(855)
Accruals released			(142)
Restructuring liability			0	0
September 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring liability		$ 0	0
Costs incurred			1,275
Restructuring cash payments			(431)
Accruals released			(27)
Restructuring liability			$ 817	$ 0