Description of Business and Summary of Significant Accounting Policies (Accounts Receivables and Allowances) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred revenue included in accounts receivables	$ 5,200	$ 6,000
Trade account receivable	117,838	62,713
Allowance for doubtful accounts	4,143	2,833
Bad debt expense	1,713	1,515	$ 3,111
Billed Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade account receivable	94,500	51,800
Unbilled Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade account receivable	$ 23,300	$ 10,900