Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2019		Apr. 30, 2018		Apr. 30, 2017
Computation of basic and diluted earnings per share of common stock
Net income	$ 16,625	$ 5,815	$ 24,912	$ 8,650	$ 9,919	$ 19,686	$ 18,023	$ 15,343	$ 56,002		$ 62,971		$ 48,886
Less: Net income allocated to participating securities									1,382
Net income attributable to common stockholders									$ 54,620		$ 62,971		$ 48,886
Basic earnings per common share:
Basic weighted average common shares outstanding (in shares)	40,487	40,912	41,149	41,094	41,048	41,036	41,006	40,971	40,914		41,015		40,260
Basic earnings per common share (in dollars per share)	$ 0.40	$ 0.14	$ 0.59	$ 0.21	$ 0.24	$ 0.48	$ 0.44	$ 0.37	$ 1.33	[1]	$ 1.54	[1]	$ 1.21	[1]
Diluted earnings per common share:
Basic weighted average common shares outstanding (in shares)	40,487	40,912	41,149	41,094	41,048	41,036	41,006	40,971	40,914		41,015		40,260
Add: Common Stock Equivalents									675		1,148		810
Diluted weighted average common shares outstanding (in shares)	40,976	41,371	41,918	42,074	42,151	42,228	42,146	42,128	41,589		42,163		41,070
Diluted earnings per common share (in dollars per share)	$ 0.39	$ 0.14	$ 0.58	$ 0.20	$ 0.24	$ 0.47	$ 0.43	$ 0.36	$ 1.31	[1]	$ 1.49	[1]	$ 1.19	[1]
Shares were not included in the calculation of Diluted loss per common share
Anti-dilutive shares									600

[1] See Note 18 for detailed calculations.