Employee Benefit Plan - Narrative (Details) - USD ($)		12 Months Ended
	Jan. 01, 2015	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Percent vested		100.00%
Matching contributions		$ 0
Mandiant, Inc.
Defined Benefit Plan Disclosure [Line Items]
Percent vested		100.00%
Matching contributions		$ 0	$ 2,900,000
Percent match of the first 4% of an eligible employee's compensation contributed		100.00%
Maximum percent of an eligible employee's compensation for 100% employer match		4.00%
Mandiant 401(k) plan
Defined Benefit Plan Disclosure [Line Items]
Matching contributions	$ 0