Commitments and Contingencies (Details)	12 Months Ended
	Apr. 30, 2018 USD ($)	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)	Jan. 01, 2019 JPY (¥)	Jan. 01, 2019 USD ($)	Dec. 27, 2017 JPY (¥)	Dec. 27, 2017 USD ($)
Future minimum lease payments under noncancelable operating leases
2018	$ 4,940,000
2019	4,774,000
2020	3,872,000
2021	3,421,000
2022	2,278,000
Thereafter	1,914,000
Total	21,199,000
Future minimum lease payments under non cancellable capital leases
2018	161,000
Total	161,000
Present value of capital lease obligations	161,000
Less: Current portion	(161,000)
Long-term portion of capital lease obligations		$ 161,000
Rental expense under operating leases	4,011,000	3,849,000	$ 4,077,000
Letters of credit outstanding	6,389,000	1,935,000
Reserve for incurred cost claim audits	$ 77,000	$ 0
HAPSMobile
Future minimum lease payments under non cancellable capital leases
Equity Method Investment, Aggregate Cost						¥ 210,000,000	$ 1,860,000
HAPSMobile | Expected
Future minimum lease payments under non cancellable capital leases
Equity Method Investment, Aggregate Cost				¥ 209,500,000	$ 1,900,000