Earnings Per Common Share - Additional Information (Detail) - $ / shares	3 Months Ended
Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Line Items]
Options to Purchase Excluded	1,024,917	855,439
Options to Purchase Outstanding	3,833,630	3,599,581
Class A Common Shares
Earnings Per Share [Line Items]
Dividends preference, per share	$ 0.05

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration