Organization and Significant Accounting Policies - Revenue by Category (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 25, 2020	Jan. 26, 2019	Jan. 25, 2020	Jan. 26, 2019
Disaggregation of revenue
Revenue	$ 61,891,000	$ 75,322,000	$ 232,073,000	$ 226,344,000
Contract Liability
Disaggregation of revenue
Revenue	12,000	10,000	1,670,000	1,587,000
Domestic
Disaggregation of revenue
Revenue	27,626,000	34,436,000	116,399,000	116,514,000
International
Disaggregation of revenue
Revenue	34,265,000	40,886,000	115,674,000	109,830,000
U.S. government
Disaggregation of revenue
Revenue	25,535,000	52,383,000	124,971,000	135,232,000
Non-U.S. government
Disaggregation of revenue
Revenue	36,356,000	22,939,000	107,102,000	91,112,000
FFP
Disaggregation of revenue
Revenue	40,145,000	52,833,000	168,607,000	160,890,000
CPFF
Disaggregation of revenue
Revenue	20,863,000	22,370,000	60,384,000	65,223,000
T&M
Disaggregation of revenue
Revenue	883,000	119,000	3,082,000	231,000
Small UAS
Disaggregation of revenue
Revenue	36,965,000	47,704,000	162,868,000	131,119,000
TMS
Disaggregation of revenue
Revenue	7,908,000	11,270,000	21,419,000	49,055,000
HAPS
Disaggregation of revenue
Revenue	11,762,000	13,586,000	37,490,000	37,981,000
Other
Disaggregation of revenue
Revenue	$ 5,256,000	$ 2,762,000	$ 10,296,000	$ 8,189,000