Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 366,786	$ 387,763
Allowance for doubtful accounts	(1,127)	(906)
Reserve for cash-basis customers	(7,662)	(6,458)
Total accounts receivable reserves	(8,789)	(7,364)
Accounts receivable, net	357,997	380,399
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	111,550	124,878
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 255,236	$ 262,885