Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 460,406	$ 374,741
Allowance for doubtful accounts	(1,043)	(829)
Reserve for cash-basis customers	(236)	(5,316)
Total accounts receivable reserves	(1,279)	(6,145)
Accounts receivable, net	459,127	368,596
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	319,996	260,976
Unbilled Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 140,410	$ 113,765