Discontinued Operations (Financial Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations	$ (15,856)	$ 29,848	$ 1,208	$ 8,487	$ 12,908	$ 11,921	$ 7,440	$ 7,709	$ 23,687	$ 39,978	$ 17,036
DMT | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue									211,542	426,676	425,252
Earnings from discontinued operations									18,952	61,074	41,880
Gain on sale									60,611	0	0
Income from discontinued operations before taxes									79,563	61,074	41,880
Tax provision									55,876	21,096	24,844
Income from discontinued operations									$ 23,687	$ 39,978	$ 17,036