Basis of Presentation - Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net income (loss) attributable to Engility	$ (16,757)	$ 3,650	$ (17,493)	$ 3,379
Weighted average number of shares outstanding – Basic	36,735	36,623	36,726	32,527
Dilutive effect of share-based compensation outstanding after application of the treasury stock method		513		538
Weighted average number of shares outstanding – Diluted	36,735	37,136	36,726	33,065
Earnings (loss) per share attributable to Engility
Basic	$ (0.46)	$ 0.10	$ (0.48)	$ 0.10
Diluted	$ (0.46)	$ 0.10	$ (0.48)	$ 0.10