Segments - Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Service revenue, net	$ 367,815	$ 336,696
Service expense	340,498	303,115
General and administrative expense	19,401	17,898
Depreciation and amortization	4,475	3,580
Operating income	3,441	12,103
Equity in net loss of investee	(1,656)	(2,321)
NET Services
Segment Reporting Information [Line Items]
Service revenue, net	367,815	336,696
Continuing operations
Segment Reporting Information [Line Items]
Service revenue, net	367,815	336,696
Service expense	340,498	303,115
General and administrative expense	19,401	17,898
Depreciation and amortization	4,475	3,580
Operating income	3,441	12,103
Equity in net loss of investee	(1,656)	(2,344)
Total assets (continuing operations)	608,827
Continuing operations | NET Services
Segment Reporting Information [Line Items]
Service revenue, net	367,815	336,696
Service expense	340,498	303,115
General and administrative expense	19,401	17,898
Depreciation and amortization	4,475	3,580
Operating income	3,441	12,103
Equity in net loss of investee	0	0
Total assets (continuing operations)	449,281
Continuing operations | Matrix Investment
Segment Reporting Information [Line Items]
Service revenue, net	0	0
Service expense	0	0
General and administrative expense	0	0
Depreciation and amortization	0	0
Operating income	0	0
Equity in net loss of investee	(1,656)	$ (2,344)
Total assets (continuing operations)	$ 159,546