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, 2018	$ 2,106,887	$ 4,214	$ 570,964	$ 2,126,790	$ (19,030)	$ (576,186)	$ 2,106,752	$ 135
Beginning balance, shares at Jun. 30, 2018		42,139				17,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	147,429			147,429			147,429
Stock-based compensation expense	12,047		12,047				12,047
Tax withholdings on restricted share vestings	(18,229)	$ 16	(18,245)				(18,229)
Tax withholdings on restricted share vestings (in shares)		157
Change in fair value of interest rate swap agreements, net	(3,561)				(3,561)		(3,561)
Currency translation adjustment	(5,431)				(5,431)		(5,431)
Repurchases of common stock	(2,756)		(185)			$ (2,571)	(2,756)
Repurchases of common stock (in shares)						15
Treasury stock issued under stock purchase plans	2,577		5			$ 2,572	2,577
Treasury stock issued under stock purchase plans (in shares)						(15)
Ending balance at Dec. 31, 2018	2,256,733	$ 4,230	564,586	2,291,989	(28,022)	$ (576,185)	2,256,598	135
Ending balance, shares at Dec. 31, 2018		42,296				17,434
Beginning balance at Sep. 30, 2018	2,190,058	$ 4,228	559,295	2,223,393	(20,808)	$ (576,185)	2,189,923	135
Beginning balance, shares at Sep. 30, 2018		42,282				17,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	68,596			68,596			68,596
Stock-based compensation expense	6,349		6,349				6,349
Tax withholdings on restricted share vestings	(993)	$ 2	(995)				(993)
Tax withholdings on restricted share vestings (in shares)		14
Change in fair value of interest rate swap agreements, net	(3,778)				(3,778)		(3,778)
Currency translation adjustment	(3,436)				(3,436)		(3,436)
Repurchases of common stock	(1,363)		(63)			$ (1,300)	(1,363)
Repurchases of common stock (in shares)						7
Treasury stock issued under stock purchase plans	1,300					$ 1,300	1,300
Treasury stock issued under stock purchase plans (in shares)						(7)
Ending balance at Dec. 31, 2018	2,256,733	$ 4,230	564,586	2,291,989	(28,022)	$ (576,185)	2,256,598	135
Ending balance, shares at Dec. 31, 2018		42,296				17,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment of ASC 606, net of taxes	17,770			17,770			17,770
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