Accounts Receivable (Tables)

12 Months Ended

Dec. 31, 2017

Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]

Schedule of Accounts Receivable

Net accounts receivable consisted of the following as of December 31, 2017 and 2016 (in thousands):

	December 31, 2017			December 31, 2016
Trade accounts receivable	$	319,996		$	260,976
Unbilled accounts receivable	140,410			113,765
Gross 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

Schedule of Activity in the Accounts Receivable Reserves

A summary of activity in the accounts receivable reserves for the years ended December 31, 2017, 2016 and 2015, is as follows (in thousands):

	2017			2016			2015
Beginning balance	$	6,145		$	7,364		$	9,023
Charges to income from operations	5,809			49,677			37,870
Collections from cash basis customers and write-offs	(10,675		)	(50,896		)	(39,529		)
Ending balance	$	1,279		$	6,145		$	7,364