Contract Balances (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Jan. 01, 2018		Dec. 31, 2017
Contract with Customer, Asset and Liability [Abstract]
Trade accounts receivable, net		$ 268,352	[1]	$ 301,963	[1]	$ 301,963
Contract assets	[2]	5,745		9,823
Contract liabilities		1,784	[3]	$ 5,415	[3]	$ 6,102
Change in Contract with Customer, Asset [Abstract]
Contract asset, decrease from beginning of period		4,100
Change in Contract with Customer, Liability [Abstract]
Contract liability, decrease from beginning of period		$ 3,600

[1] Includes billed and unbilled amounts, net of allowance for doubtful accounts. See Note 4 for details.

[2] Included in the “Prepaid expenses and other current assets” line on the consolidated balance sheet.

[3] Included in the “Other accrued liabilities” line of the consolidated balance sheet.