Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Depreciation of property, plant and equipment	$ 15,717	$ 16,097	$ 16,045	$ 16,761	$ 15,640	$ 14,460	$ 25,609	$ 22,197	$ 64,620	$ 77,906	$ 74,913
Interest Costs Capitalized									$ 400	$ 0	0
Higher Education [Member] | Education [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment impairment charges							$ 6,900				$ 13,600