Restatement (Details) - USD ($) $ in Thousands		3 Months Ended												6 Months Ended	9 Months Ended			12 Months Ended							18 Months Ended	21 Months Ended
		Dec. 31, 2015		Oct. 04, 2015	Jul. 05, 2015	Jul. 04, 2015	Mar. 31, 2015		Dec. 31, 2014	Sep. 28, 2014	Jun. 29, 2014	Sep. 29, 2013	Sep. 30, 2012	Oct. 04, 2015	Dec. 31, 2015		Dec. 28, 2014	Dec. 31, 2015		Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2013	Sep. 28, 2014	Dec. 31, 2014	Jul. 03, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		$ 1,670,821	[1]	$ 1,789,963			$ 1,696,529	[1]		$ 1,216,362	$ 1,240,892			$ 1,789,963	$ 1,670,821	[1]	$ 1,255,374	$ 1,670,821	[1]	$ 1,696,529	[1]				$ 1,216,362		$ 1,774,715
Sales		1,144,560		1,143,246	$ 1,103,578		971,150		$ 724,541	722,012	694,956			2,246,823	3,391,384	[2]	2,141,509			3,112,659	[2]	$ 2,890,711	[2]		1,416,968	$ 2,141,509
Cost of sales		902,090		934,429		$ 880,717	747,877		563,345	563,817	536,717			1,815,145	2,717,236	[2]				2,411,756	[2]	2,600,607	[2]		1,100,534	1,663,879
Gross profit		242,470		208,817	222,861		223,273		161,196	158,195	158,239			431,678	674,148	[2]	477,630			700,903	[2]	290,104	[2]		316,434	477,630
General and administrative		90,803		65,204		64,150	139,088		51,947	50,962	62,593			129,354	220,157	[2]				304,590	[2]	209,199	[2]		113,555	165,502
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest		94,252		136,810		101,543	3,609		76,628	75,078	67,408			238,353	332,605	[2]				222,723	[2]	(58,885)	[2]		142,486	219,114
Income from continuing operations, before income taxes and noncontrolling interest		74,302		112,174		85,759	(43,768)		55,262	51,738	44,017			197,932	272,235	[2]				107,249	[2]	(138,677)	[2]		95,755	151,017
Total current assets		2,128,479	[1]	2,368,869			2,393,523	[1]		2,538,381	2,617,093			2,368,869	2,128,479	[1]	2,619,411	2,128,479	[1]	2,393,523	[1]				2,538,381		2,346,610
Net property, plant, and equipment		761,694	[1]	750,080			769,050	[1]		478,909	480,782			750,080	761,694	[1]	479,005	761,694	[1]	769,050	[1]				478,909		758,820
Goodwill		1,828,366	[1]	1,862,255			1,862,255	[1]		1,039,763	1,039,763			1,862,255	1,828,366	[1]	1,039,763	1,828,366	[1]	1,862,255	[1]	1,039,763			1,039,763		1,862,255
Other noncurrent assets		139,462	[1]	131,354			142,461	[1]		110,075	109,543			131,354	139,462	[1]	108,954	139,462	[1]	142,461	[1]				110,075		135,678
Assets		5,323,695	[1]	5,379,362			5,477,532	[1]		5,874,197	5,974,098			5,379,362	5,323,695	[1]	5,823,906	5,323,695	[1]	5,477,532	[1]	3,490,706			5,874,197		5,398,809
Contract-related liabilities		381,712	[1]	276,441			358,518	[1]			0			276,441	381,712	[1]		381,712	[1]	358,518	[1]						312,145
Contract loss reserve		235,841	[1]	242,744			262,324	[1]		302,716	321,807			242,744	235,841	[1]	279,874	235,841	[1]	262,324	[1]				302,716		253,410
Accrued compensation		127,928	[1]	143,450			144,185	[1]		66,096	70,076			143,450	127,928	[1]	78,965	127,928	[1]	144,185	[1]				66,096		102,108
Total current liabilities		1,254,435	[1]	1,251,989			1,377,108	[1]		1,305,315	1,428,600			1,251,989	1,254,435	[1]	1,339,756	1,254,435	[1]	1,377,108	[1]				1,305,315		1,261,042
Other noncurrent liabilities		127,152	[1]	131,151			141,433	[1]		100,538	101,379			131,151	127,152	[1]	101,906	127,152	[1]	141,433	[1]				100,538		130,332
Total liabilities		3,638,257	[1]	3,746,687			3,956,136	[1]		4,119,744	4,198,496			3,746,687	3,638,257	[1]	4,028,947	3,638,257	[1]	3,956,136	[1]				4,119,744		3,807,247
Net income attributable to Orbital ATK, Inc.		54,304		74,047	$ 57,836		(22,516)		42,865	91,789	82,762			131,883	186,187	[2]	217,415			194,900	[2]	117,034	[2]		174,551	217,415
Forward loss	[3]														0					0		342,000
Goodwill impairment						0	34,300								0	[2],[3]				34,300	[2],[3]	3,700	[2],[3]
Retained earnings		1,043,043	[1]	1,010,527			894,008	[1]		2,698,127	2,616,557			1,010,527	1,043,043	[1]	2,730,772	1,043,043	[1]	894,008	[1]				2,698,127		951,825
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		1,784,434		1,882,675			1,793,556			1,288,281	1,290,540			1,882,675	1,784,434		1,352,062	1,784,434		1,793,556					1,288,281		1,891,338
Sales		1,138,238		1,134,886		1,129,957	969,539		746,866	743,202	714,360			2,264,842	3,399,089					3,173,967		2,925,237			1,457,562	2,204,428
Cost of sales		900,383		884,734		875,532	756,998		581,339	579,818	551,710			1,760,265	2,729,898					2,469,865		2,277,939			1,131,528	1,712,867
Gross profit		237,855		250,152		254,425	212,541		165,527	163,384	162,650			504,577	669,191					704,102		647,298			326,034	491,561
General and administrative		90,853		69,384		71,463	133,057		51,947	50,962	62,593			140,847	225,418					298,559		209,251			113,555	165,502
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest		89,587		123,965		125,794	(1,092)		80,959	80,267	71,819			249,759	322,387					231,953		301,957			152,086	233,045
Income from continuing operations, before income taxes and noncontrolling interest		73,016		99,672		110,433	(48,297)		59,593	56,927	48,428			210,104	265,224					116,651		222,165			105,355	164,948
Total current assets		2,240,442		2,359,972			2,388,906			2,483,653	2,540,094			2,359,972	2,240,442		2,589,452	2,240,442		2,388,906					2,483,653		2,361,597
Net property, plant, and equipment		806,187		797,524			807,057			506,083	505,947			797,524	806,187		508,583	806,187		807,057					506,083		802,134
Goodwill		1,832,066		1,875,269			1,875,269			1,043,463	1,043,463			1,875,269	1,832,066		1,043,463	1,832,066		1,875,269					1,043,463		1,875,269
Other noncurrent assets		103,680		102,026			111,074			89,420	90,750			102,026	103,680		86,756	103,680		111,074					89,420		106,962
Assets		5,339,392		5,395,394			5,487,834			5,822,986	5,900,469			5,395,394	5,339,392		5,798,325	5,339,392		5,487,834					5,822,986		5,427,366
Contract-related liabilities		340,888		268,129			357,296				0			268,129	340,888			340,888		357,296							314,642
Contract loss reserve		0		0			0			0	0			0	0		0	0		0					0		0
Accrued compensation		125,278		140,800			135,528			66,096	70,076			140,800	125,278		78,965	125,278		135,528					66,096		99,458
Total current liabilities		966,979		975,017			1,096,784			1,002,599	1,106,793			975,017	966,979		1,059,882	966,979		1,096,784					1,002,599		988,953
Other noncurrent liabilities		167,798		150,619			165,795			100,637	101,471			150,619	167,798		102,011	167,798		165,795					100,637		149,797
Total liabilities		3,391,447		3,489,183			3,700,174			3,817,127	3,876,781			3,489,183	3,391,447		3,749,178	3,391,447		3,700,174					3,817,127		3,554,623
Net income attributable to Orbital ATK, Inc.		54,237		66,402		72,753	(23,870)		45,647	95,109	85,598			139,155	182,430					202,484		340,915			180,707	226,353
Forward loss																						0
Goodwill impairment						0	34,300													34,300		0
Retained earnings		1,305,550		1,284,063			1,160,272			2,949,533	2,864,643			1,284,063	1,305,550		2,984,960	1,305,550		1,160,272					2,949,533		1,233,006
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		(113,613)					(97,027)			(71,919)	(49,648)				(113,613)		(96,688)	(113,613)		(97,027)					(71,919)
Sales		6,322					1,611		(22,325)	(21,190)	(19,404)				(7,705)					(61,308)		(34,526)			(40,594)	(62,919)
Cost of sales		1,707					(9,121)		(17,994)	(16,001)	(14,993)				(12,662)					(58,109)		322,668			(30,994)	(48,988)
Gross profit		4,615					10,732		(4,331)	(5,189)	(4,411)				4,957					(3,199)		(357,194)			(9,600)	(13,931)
General and administrative		(50)					6,031		0	0	0				(5,261)					6,031		(52)			0	0
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest		4,665					4,701		(4,331)	(5,189)	(4,411)				10,218					(9,230)		(360,842)			(9,600)	(13,931)
Income from continuing operations, before income taxes and noncontrolling interest		1,286					4,529		(4,331)	(5,189)	(4,411)				7,011					(9,402)		(360,842)			(9,600)	(13,931)
Total current assets		(111,963)					4,617			54,728	76,999				(111,963)		29,959	(111,963)		4,617					54,728
Net property, plant, and equipment		(44,493)					(38,007)			(27,174)	(25,165)				(44,493)		(29,578)	(44,493)		(38,007)					(27,174)
Goodwill		(3,700)					(13,014)			(3,700)	(3,700)				(3,700)		(3,700)	(3,700)		(13,014)					(3,700)
Other noncurrent assets		35,782					31,387			20,655	18,793				35,782		22,198	35,782		31,387					20,655
Assets		(15,697)					(10,302)			51,211	73,629				(15,697)		25,581	(15,697)		(10,302)					51,211
Contract-related liabilities		40,824					1,222				0				40,824			40,824		1,222
Contract loss reserve		235,841					262,324			302,716	321,807				235,841		279,874	235,841		262,324					302,716
Accrued compensation		2,650					8,657			0	0				2,650		0	2,650		8,657					0
Total current liabilities		287,456					280,324			302,716	321,807				287,456		279,874	287,456		280,324					302,716
Other noncurrent liabilities		(40,646)					(24,362)			(99)	(92)				(40,646)		(105)	(40,646)		(24,362)					(99)
Total liabilities		246,810					255,962			302,617	321,715				246,810		279,769	246,810		255,962					302,617
Net income attributable to Orbital ATK, Inc.		67					1,354		$ (2,782)	(3,320)	(2,836)				3,757					(7,584)		(223,881)			(6,156)	$ (8,938)
Forward loss																						342,000
Goodwill impairment							0													0		3,700
Retained earnings		(262,507)					(266,264)			$ (251,406)	$ (248,086)				(262,507)		$ (254,188)	(262,507)		(266,264)					$ (251,406)
Lake City Contract Loss and Related Adjustments: | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		(105,529)					(92,534)								(105,529)			(105,529)		(92,534)
Sales															(12,995)					(58,008)		(34,526)
Cost of sales															(24,911)					(57,567)		322,495
Gross profit															11,916					(441)		(357,021)
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest															11,916					(441)		(360,721)
Income from continuing operations, before income taxes and noncontrolling interest															11,916					(441)		(360,721)
Total current assets		(105,529)					(92,534)								(105,529)			(105,529)		(92,534)
Net property, plant, and equipment		(41,855)					(37,594)								(41,855)			(41,855)		(37,594)
Assets		(151,084)					(133,828)								(151,084)			(151,084)		(133,828)
Contract loss reserve		229,663					258,834								229,663			229,663		258,834
Total current liabilities		229,663					258,834								229,663			229,663		258,834
Total liabilities		229,663					258,834								229,663			229,663		258,834
Contract Loss Reserve Adjustment: | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		759					545								759			759		545
Sales															0					0		0
Cost of sales															2,474					(743)		182
Gross profit															(2,474)					743		(182)
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest															(2,474)					743		(182)
Income from continuing operations, before income taxes and noncontrolling interest															(2,474)					743		(182)
Total current assets		759					545								759			759		545
Net property, plant, and equipment		0					0								0			0		0
Assets		759					545								759			759		545
Contract loss reserve		6,178					3,490								6,178			6,178		3,490
Total current liabilities		6,178					3,490								6,178			6,178		3,490
Total liabilities		6,178					3,490								6,178			6,178		3,490
Account Review and Analysis Adjustments | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables		(8,843)					(5,038)								(8,843)			(8,843)		(5,038)
Sales															5,290					(3,300)		0
Cost of sales															9,775					201		(9)
Gross profit															(4,485)					(3,501)		9
General and administrative															(5,261)					6,031		(52)
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest															776					(9,532)		61
Income from continuing operations, before income taxes and noncontrolling interest															(2,431)					(9,704)		61
Total current assets		(7,174)					(7,631)								(7,174)			(7,174)		(7,631)
Net property, plant, and equipment		(2,639)					(413)								(2,639)			(2,639)		(413)
Goodwill		0					(9,314)								0			0		(9,314)
Other noncurrent assets		(6,773)					(7,005)								(6,773)			(6,773)		(7,005)
Assets		(15,671)					(30,380)								(15,671)			(15,671)		(30,380)
Contract-related liabilities		40,824					1,222								40,824			40,824		1,222
Accrued compensation		2,650					8,657								2,650			2,650		8,657
Total current liabilities		51,634					18,000								51,634			51,634		18,000
Other noncurrent liabilities		(40,434)					(24,173)								(40,434)			(40,434)		(24,173)
Total liabilities		$ 11,200					(6,173)								$ 11,200			11,200		(6,173)
First Restatement Adjustments | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables				15,986										15,986													(13,719)
Sales				18,731		(22,723)								(3,992)
Cost of sales				58,408		10,841								69,249
Gross profit				(39,677)		(33,564)								(73,241)
General and administrative				(4,180)		(2,102)								(6,282)
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest				14,503		(31,462)								(16,959)
Income from continuing operations, before income taxes and noncontrolling interest				14,160		(32,057)								(17,897)
Total current assets				15,986										15,986													(13,719)
Net property, plant, and equipment				(4,200)										(4,200)													(2,100)
Goodwill				(9,314)										(9,314)													(9,314)
Other noncurrent assets				0										0													0
Assets				(2,107)										(2,107)													(21,847)
Contract-related liabilities				(13,274)										(13,274)													(27,783)
Contract loss reserve				0										0													0
Accrued compensation				0										0													0
Total current liabilities				2,601										2,601													(12,167)
Other noncurrent liabilities				6,254										6,254													9,955
Total liabilities				8,855										8,855													(2,212)
Net income attributable to Orbital ATK, Inc.				8,673		(19,635)								(10,962)
Goodwill impairment						0
Retained earnings				(10,962)										(10,962)													(19,635)
Second Restatement Adjustments | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net receivables				(108,698)										(108,698)													(102,904)
Sales				(10,371)		(3,656)								(14,027)
Cost of sales				(8,713)		(5,656)								(14,369)
Gross profit				(1,658)		2,000								342
General and administrative				0		(5,211)								(5,211)
Income (loss) from continuing operations, before interest, income taxes and noncontrolling interest				(1,658)		7,211								5,553
Income from continuing operations, before income taxes and noncontrolling interest				(1,658)		7,383								5,725
Total current assets				(7,089)										(7,089)													(1,268)
Net property, plant, and equipment				(43,244)										(43,244)													(41,214)
Goodwill				(3,700)										(3,700)													(3,700)
Other noncurrent assets				29,328										29,328													28,716
Assets				(13,925)										(13,925)													(6,710)
Contract-related liabilities				21,586										21,586													25,286
Contract loss reserve				242,744										242,744													253,410
Accrued compensation				2,650										2,650													2,650
Total current liabilities				274,371										274,371													284,256
Other noncurrent liabilities				(25,722)										(25,722)													(29,420)
Total liabilities				248,649										248,649													254,836
Net income attributable to Orbital ATK, Inc.				(1,028)		4,718								3,690
Goodwill impairment						$ 0
Retained earnings				$ (262,574)										$ (262,574)													$ (261,546)
U.S. Army | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Term of contract, additional term															3 years
Initial term of contract															7 years
Forward loss												$ 342,000	$ 31,500
Goodwill impairment																								$ 3,700
Impairment of long lived assets															$ 7,619					17,559		$ 23,369
Increase in contract loss reserve liability							$ 2,945											$ 5,419
Income (Loss) from continuing operations before income taxes, extraordinary items, noncontrolling interest															$ 8,000					$ (8,471)
Retained earnings																								$ (21,000)

[1] See Note 2 - Restatement

[2] See Note 2 - Restatement

[3] See Note 2 - Restatement