Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Computation of basic and diluted earnings per share of common stock
Net income									$ 62,971	$ 48,886	$ 12,564
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)					40,956	40,943	40,943	38,201	41,015,000	40,260,000	32,799,000
Basic earnings per common share (in dollars per share)					$ 0.35	$ 0.20	$ 0.42	$ 0.24	$ 1.54	$ 1.21	$ 0.38
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)					40,956	40,943	40,943	38,201	41,015,000	40,260,000	32,799,000
Add: Common Stock Equivalents									1,148,000	810,000	326,000
Diluted weighted average common shares outstanding (in shares)	41,048	41,036	41,006	40,971	41,759	41,578	41,320	38,602	42,163,000	41,070,000	33,125,000
Diluted earnings per common share (in dollars per share)	$ 0.24	$ 0.48	$ 0.44	$ 0.37	$ 0.33	$ 0.20	$ 0.42	$ 0.24	$ 1.49	$ 1.19	$ 0.38