Description of Business and Summary of Significant Accounting Policies (Accounts Receivables and Allowances) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 162,155		$ 174,340
Allowance for doubtful accounts	6,619		$ 6,969
Deferred revenue included in accounts receivables	8,000
Provision for doubtful accounts	134	$ 1,045
Allowance for Doubtful Accounts Receivable, Write-offs	484	$ 40
Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	131,200
Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 31,000