Acquisitions - Schedule of Business Acquisition, By Acquisition (Details) - USD ($) $ in Thousands	Aug. 31, 2017	Apr. 01, 2017	Feb. 01, 2017	Sep. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill				$ 144,374	$ 127,772
YouTrain
Business Acquisition [Line Items]
Cash purchase price	$ 4,898
Estimated completion accounts payment	180
Total purchase price	5,078
Cash	673
Accounts Receivable, Gross, Current	248
Fixed assets	215
Goodwill	3,228
Total assets	5,677
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	322
Billings in excess of costs and estimated earnings on uncompleted contracts	28
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	249
Total liabilities	599
Net assets acquired	5,078
McKinney Rogers
Business Acquisition [Line Items]
Cash purchase price			$ 3,259
Fair value of contingent consideration			4,505
Total purchase price			7,764
Goodwill			5,196
Total assets			8,674
Accrued expenses			44
Billings in excess of costs and estimated earnings on uncompleted contracts			866
Total liabilities			910
Net assets acquired			7,764
Emantras
Business Acquisition [Line Items]
Cash purchase price		$ 3,191
Fair value of contingent consideration		220
Total purchase price		3,411
Fixed assets		50
Goodwill		3,156
Total assets		4,024
Accrued expenses		558
Billings in excess of costs and estimated earnings on uncompleted contracts		55
Total liabilities		613
Net assets acquired		3,411
Customer relationships | YouTrain
Business Acquisition [Line Items]
Intangible assets, other than goodwill	$ 1,313
Acquired finite-lived intangible assets, weighted average useful life	5 years
Customer relationships | McKinney Rogers
Business Acquisition [Line Items]
Intangible assets, other than goodwill			$ 653
Acquired finite-lived intangible assets, weighted average useful life			5 years
Customer relationships | Emantras
Business Acquisition [Line Items]
Intangible assets, other than goodwill		$ 818
Acquired finite-lived intangible assets, weighted average useful life		4 years
Marketing-Related Intangible Assets | McKinney Rogers
Business Acquisition [Line Items]
Intangible assets, other than goodwill			$ 121
Acquired finite-lived intangible assets, weighted average useful life			3 years
Technology-Based Intangible Assets | McKinney Rogers
Business Acquisition [Line Items]
Intangible assets, other than goodwill			$ 2,704
Acquired finite-lived intangible assets, weighted average useful life			5 years