Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 374,741	$ 387,763
Allowance for doubtful accounts	(829)	(906)
Reserve for cash-basis customers	(5,316)	(6,458)
Total accounts receivable reserves	(6,145)	(7,364)
Accounts receivable, net	368,596	380,399
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	260,976	262,885
Unbilled Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 113,765	$ 124,878