Accounts Receivable, net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled revenues accrued	$ 32,300			$ 16,100		$ 32,300
Bad debt provision (reversal) for doubtful accounts receivables	$ 0				$ 0	$ 2,798	$ 0
Renewable Energy Industry Customer | Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bad debt provision (reversal) for doubtful accounts receivables		$ (1,000)	$ 5,700	$ (700)
Recovery from unrelated bad debt provision		$ 1,700	$ 200