Investments - Held-To-Maturity Securities (Details) $ in Thousands	Apr. 30, 2017 USD ($)
Held To Maturity Securities
Amortized Cost	$ 159,570
Gross Unrealized Gains	42
Gross Unrealized Losses	(147)
Fair Value	159,465
Municipal securities
Held To Maturity Securities
Amortized Cost	56,379
Gross Unrealized Gains	30
Gross Unrealized Losses	(21)
Fair Value	56,388
U.S. government securities
Held To Maturity Securities
Amortized Cost	37,055
Gross Unrealized Gains	2
Gross Unrealized Losses	(41)
Fair Value	37,016
Corporate bonds
Held To Maturity Securities
Amortized Cost	63,636
Gross Unrealized Gains	9
Gross Unrealized Losses	(85)
Fair Value	63,560
Certificates of deposit
Held To Maturity Securities
Amortized Cost	2,500
Gross Unrealized Gains	1
Fair Value	$ 2,501