Fair Value (Changes in Deferred Contingent Consideration Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Contingent Consideration [Line Items]
Beginning Balance	$ 1,723	$ 8,782
Acquisitions		1,668
Accretion of acquisition-related contingent consideration	264	771
Remeasurement of acquisition-related contingent consideration	2,213	1,330	$ (13,047)
Payments of contingent acquisition liabilities	(10,330)	(828)	(4,592)
Reclassification to definitive consideration liability		(10,000)
Ending Balance	3,870	$ 1,723	$ 8,782
Other Acquisitions [Member]
Business Acquisition, Contingent Consideration [Line Items]
Payments of contingent acquisition liabilities	$ (330)