Fair Value Measurements (Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
fairvalueadjustmentforcontingentconsideration		$ 0	$ 613
Contingent consideration for acquisitions
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	$ 5,843		21,594
Contingent Consideration Liability [Member]
Contingent consideration for acquisitions
Balance at beginning of period	(5,843)		(20,981)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0		(613)
Balance at end of period	$ 0		$ 0