Investments - Held-To-Maturity Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2020	Apr. 30, 2019
Investments
Carrying Amount	$ 151,867
Net Unrealized Gains	150
Held To Maturity Securities
Amortized Cost	58,032
Total	58,095
Municipal securities
Investments
Carrying Amount	23,706
Net Unrealized Gains	34
U.S. government securities
Investments
Carrying Amount	41,465
Net Unrealized Gains	38
Corporate bonds
Investments
Carrying Amount	85,679
Net Unrealized Gains	73
Certificates of deposit
Investments
Carrying Amount	1,017
Net Unrealized Gains	5
Held to maturity securities
Held To Maturity Securities
Amortized Cost	159,873
Gross Unrealized Gains	100
Gross Unrealized Losses	(58)
Total	159,915
Held to maturity securities \| Municipal securities
Held To Maturity Securities
Amortized Cost	5,332
Gross Unrealized Gains	2
Gross Unrealized Losses	(1)
Total	5,333
Held to maturity securities \| U.S. government securities
Held To Maturity Securities
Amortized Cost	70,609
Gross Unrealized Gains	78
Gross Unrealized Losses	(52)
Total	70,635
Held to maturity securities \| Corporate bonds
Held To Maturity Securities
Amortized Cost	83,932
Gross Unrealized Gains	20
Gross Unrealized Losses	(5)
Total	83,947
Available-for-sale securities
Held To Maturity Securities
Amortized Cost	58,032
Gross Unrealized Gains	70
Gross Unrealized Losses	(7)
Total	58,095	$ 0
Available-for-sale securities \| Municipal securities
Held To Maturity Securities
Amortized Cost	6,807
Gross Unrealized Gains	29
Total	6,836
Available-for-sale securities \| U.S. government securities
Held To Maturity Securities
Amortized Cost	42,730
Gross Unrealized Gains	41
Gross Unrealized Losses	(4)
Total	42,767
Available-for-sale securities \| Corporate bonds
Held To Maturity Securities
Amortized Cost	8,495
Gross Unrealized Losses	(3)
Total	$ 8,492

Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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-Subparagraph (b)
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