Condensed Parent Company Financial Information - Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Condensed Parent Company Statements of Operations and Comprehensive Income (Loss)
Net income (loss)	$ 14,273	$ 8,226	$ 17,224	$ 9,163	$ 8,940	$ (2,212)	$ 2,825	$ 3,011	$ 48,886	$ 12,564	$ (11,697)
Comprehensive income (loss)									$ 49,150	$ 11,406	$ (11,687)
Weighted average shares outstanding:
Basic (in shares)	40,955,632	40,942,905	40,942,905	38,200,597	32,892,905	32,890,930	32,737,956	32,677,418	40,260,405	32,799,098	32,450,401
Diluted (in shares)	41,758,974	41,577,675	41,319,651	38,602,378	33,155,140	32,890,930	32,898,075	32,830,677	41,070,025	33,125,242	32,450,401
Net income (loss) per share:
Basic (in dollars per share)	$ 0.35	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.21	$ 0.38	$ (0.36)
Diluted (in dollars per share)	$ 0.33	$ 0.20	$ 0.42	$ 0.24	$ 0.27	$ (0.07)	$ 0.09	$ 0.09	$ 1.19	$ 0.38	$ (0.36)
Parent Company
Condensed Parent Company Statements of Operations and Comprehensive Income (Loss)
Net income (loss) in subsidiaries									$ 48,886	$ 12,564	$ (11,697)
Net income (loss)									48,886	12,564	(11,697)
Comprehensive income (loss)									$ 49,150	$ 11,406	$ (11,687)
Weighted average shares outstanding:
Basic (in shares)									40,260,405	32,799,098	32,450,401
Diluted (in shares)									41,070,025	33,125,242	32,450,401
Net income (loss) per share:
Basic (in dollars per share)									$ 1.21	$ 0.38	$ (0.36)
Diluted (in dollars per share)									$ 1.19	$ 0.38	$ (0.36)