Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities [Line Items]
Provision for credit losses	$ (7,700)	$ 1,600
Contract liabilities	259,488		$ 228,388
Contract with customer liability, deferred revenue current	240,800		$ 203,000
Deferred revenue, revenue recognized	146,800	105,600
Non-recourse financing agreement, discount charge	(12,459)	(17,004)
Receivables, Non-Recourse Arrangement [Member]
Schedule of Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities [Line Items]
Non-recourse financing agreement, discount charge	$ (800)	$ (1,800)
Minimum [Member]
Schedule of Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities [Line Items]
Retainage, percentage of contract billings	5.00%
Maximum [Member]
Schedule of Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities [Line Items]
Retainage, percentage of contract billings	10.00%