Acquisitions (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 01, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Purchase price allocation:
Goodwill		$ 127,772	$ 121,975	$ 125,757
Acquired finite-lived intangible assets, weighted average useful life		2 years 5 months
Maverick Solutions [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 4,639
Fair value of contingent consideration	5,166
Total purchase price	9,805
Purchase price allocation:
Fixed assets	63
Goodwill	8,111
Total assets	10,166
Accrued expenses	38
Billings in excess of costs and estimated earnings on uncompleted contracts	323
Total liabilities	361
Net assets acquired	9,805
Maverick Solutions [Member] | Customer-related intangible assets [Member]
Purchase price allocation:
Intangible assets	$ 1,219
Acquired finite-lived intangible assets, weighted average useful life	4 years
Maverick Solutions [Member] | Marketing-related intangible assets [Member]
Purchase price allocation:
Intangible assets	$ 124
Acquired finite-lived intangible assets, weighted average useful life	2 years
Maverick Solutions [Member] | Technology-related intangible assets [Member]
Purchase price allocation:
Intangible assets	$ 649
Acquired finite-lived intangible assets, weighted average useful life	3 years