Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 01, 2012	Jan. 02, 2011	Jan. 01, 2012	Jan. 02, 2011	Mar. 31, 2011
Comprehensive Income.
Net income	$ 49,759	$ 70,276	$ 201,561	$ 242,439
Other comprehensive (loss) income:
Pension and other postretirement benefit liabilities, net of income taxes of $(8,724), $(7,539), $(26,173), and $(22,804), respectively	13,812	12,366	41,436	36,860
Pension and other postretirement benefit liabilities, tax	(8,724)	(7,539)	(26,173)	(22,804)
Change in fair value of derivatives, net of income taxes of $(3,875), $(6,210), $20,495, and $169, respectively	6,061	9,711	(32,056)	(264)
Change in fair value of derivatives, tax	(3,875)	(6,210)	20,495	169
Change in fair value of available-for-sale securities, net of income taxes of $60, $(43), $34 and $83, respectively	(95)	67	(54)	(130)
Change in fair value of available-for-sale securities, tax	60	(43)	34	83
Total other comprehensive income	19,778	22,144	9,326	36,466
Comprehensive income	69,537	92,420	210,887	278,905
Comprehensive income attributable to noncontrolling interest	74	95	368	367
Comprehensive income attributable to Alliant Techsystems Inc.	69,463	92,325	210,519	278,538
Components of accumulated OCI, net of income taxes
Derivatives	(1,957)		(1,957)		30,099
Pension and other postretirement benefit liabilities	(776,980)		(776,980)		(818,416)
Available-for-sale securities	1,186		1,186		1,240
Total accumulated other comprehensive loss	(777,751)		(777,751)		(787,077)
Pre-tax activity in OCI related to the forward contracts
Beginning of period unrealized gain in accumulated OCI	(13,080)	50,797	49,408	65,582
(Decrease) Increase in fair value of derivatives	12,845	26,610	(30,413)	28,630
Gains reclassified from OCI, offsetting the price paid to suppliers	(2,908)	(12,747)	(22,138)	(29,552)
End of period unrealized (loss) gain in accumulated OCI	$ (3,143)	$ 64,660	$ (3,143)	$ 64,660