CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total CACI Shareholders' Equity	Noncontrolling Interest
Beginning balance at Jun. 30, 2019	$ 2,371,466	$ 4,231	$ 576,277	$ 2,410,164	$ (43,156)	$ (576,185)	$ 2,371,331	$ 135
Beginning balance, shares at Jun. 30, 2019		42,314				17,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	147,172			147,172			147,172
Stock-based compensation expense	14,499		14,499				14,499
Tax withholdings on restricted share vestings	(29,070)	$ 19	(29,089)				(29,070)
Tax withholdings on restricted share vestings (in shares)		191
Change in fair value of interest rate swap agreements, net	(1,229)				(1,229)		(1,229)
Currency translation adjustment	5,907				5,907		5,907
Repurchases of common stock	(3,596)		(179)			$ (3,417)	(3,596)
Repurchases of common stock (in shares)						17
Treasury stock issued under stock purchase plans	3,431		13			$ 3,418	3,431
Treasury stock issued under stock purchase plans (in shares)						(17)
Ending balance at Dec. 31, 2019	2,508,580	$ 4,250	561,521	2,557,336	(38,478)	$ (576,184)	2,508,445	135
Ending balance, shares at Dec. 31, 2019		42,505				17,434
Beginning balance at Sep. 30, 2019	2,425,251	$ 4,239	572,348	2,478,141	(53,428)	$ (576,184)	2,425,116	135
Beginning balance, shares at Sep. 30, 2019		42,392				17,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	79,195			79,195			79,195
Stock-based compensation expense	7,461		7,461				7,461
Tax withholdings on restricted share vestings	(18,210)	$ 11	(18,221)				(18,210)
Tax withholdings on restricted share vestings (in shares)		113
Change in fair value of interest rate swap agreements, net	3,735				3,735		3,735
Currency translation adjustment	11,215				11,215		11,215
Repurchases of common stock	(1,879)		(67)			$ (1,812)	(1,879)
Repurchases of common stock (in shares)						9
Treasury stock issued under stock purchase plans	1,812					$ 1,812	1,812
Treasury stock issued under stock purchase plans (in shares)						(9)
Ending balance at Dec. 31, 2019	2,508,580	$ 4,250	561,521	2,557,336	(38,478)	$ (576,184)	2,508,445	135
Ending balance, shares at Dec. 31, 2019		42,505				17,434
Beginning balance at Jun. 30, 2020	2,661,310	$ 4,253	573,744	2,731,644	(72,285)	$ (576,181)	2,661,175	135
Beginning balance, shares at Jun. 30, 2020		42,525				17,432
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	200,122			200,122			200,122
Stock-based compensation expense	15,041		15,041				15,041
Tax withholdings on restricted share vestings	(18,582)	$ 13	(18,595)				(18,582)
Tax withholdings on restricted share vestings (in shares)		138
Change in fair value of interest rate swap agreements, net	4,896				4,896		4,896
Currency translation adjustment	21,506				21,506		21,506
Repurchases of common stock	(4,420)		(33)			$ (4,387)	(4,420)
Repurchases of common stock (in shares)						22
Treasury stock issued under stock purchase plans	4,406		19			$ 4,387	4,406
Treasury stock issued under stock purchase plans (in shares)						(22)
Ending balance at Dec. 31, 2020	2,884,279	$ 4,266	570,176	2,931,766	(45,883)	$ (576,181)	2,884,144	135
Ending balance, shares at Dec. 31, 2020		42,663				17,432
Beginning balance at Sep. 30, 2020	2,771,769	$ 4,254	580,513	2,825,288	(62,240)	$ (576,181)	2,771,634	135
Beginning balance, shares at Sep. 30, 2020		42,537				17,432
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	106,478			106,478			106,478
Stock-based compensation expense	7,194		7,194				7,194
Tax withholdings on restricted share vestings	(17,406)	$ 12	(17,418)				(17,406)
Tax withholdings on restricted share vestings (in shares)		126
Change in fair value of interest rate swap agreements, net	2,644				2,644		2,644
Currency translation adjustment	13,713				13,713		13,713
Repurchases of common stock	(2,346)		(113)			$ (2,233)	(2,346)
Repurchases of common stock (in shares)						12
Treasury stock issued under stock purchase plans	2,233					$ 2,233	2,233
Treasury stock issued under stock purchase plans (in shares)						(12)
Ending balance at Dec. 31, 2020	$ 2,884,279	$ 4,266	$ 570,176	$ 2,931,766	$ (45,883)	$ (576,181)	$ 2,884,144	$ 135
Ending balance, shares at Dec. 31, 2020		42,663				17,432