Description of Business and Summary of Significant Accounting Policies (Fair Value Reporting) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Total assets measured at fair value	[1]	$ 31,873	$ 28,571
Total liabilities measured at fair value	[1]	24,976	37,096
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation:
Beginning balance		37,096	8,510
(Gains) or losses included in earnings	[2]	(1,391)	(164)
Reductions recorded against goodwill		(13,718)	(4,007)
Foreign currency translation adjustments	[3]	(1,620)	522
Business acquisitions		8,440	34,156
Settlements		(3,831)	(1,921)
Ending balance		24,976	37,096
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability, gain (loss) included in earnings, unrealized still held at year end		$ (1,391)	0
Derivative
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Input, Discount Rate		13.50%
Contingent Accrued Earn-out Acquisition Consideration
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivative liabilities	[1],[4]	$ 24,976	37,096
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation:
Beginning balance		37,100
Ending balance		24,980	37,100
Certificates of Deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	[1]	26,714	22,293
Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	[1]	5,159	6,278
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Total assets measured at fair value	[1]	31,873	28,571
Fair Value, Inputs, Level 1 | Certificates of Deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	[1]	26,714	22,293
Fair Value, Inputs, Level 1 | Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	[1]	5,159	6,278
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Total liabilities measured at fair value	[1]	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Total liabilities measured at fair value	[1]	24,976	37,096
Fair Value, Inputs, Level 3 | Contingent Accrued Earn-out Acquisition Consideration
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivative liabilities	[1],[4]	24,976	37,096
Certificates of Deposit | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities, Noncurrent		680	2,190
Mutual Funds | Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities		$ 5,159	$ 785

[1] During the year ended December 31, 2018 and 2017, respectively, there were no transfers between fair value levels 1, 2, or 3.

[2] Recorded as an adjustment to reported general and administrative expenses

[3] Recorded as a component of other comprehensive income within stockholders' equity

[4] The income valuation approach is applied and the valuation inputs include the contingent payment arrangement terms, projected cash flows, rate of return, and probability assessments.