Shareholders' Equity - Additional Information (Detail) - USD ($)	12 Months Ended			152 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2015
Stock Based Compensation And Stockholders Equity [Line Items]
Incentive and nonqualified options exercisable	1,203,369			1,203,369
Weighted-average grant date fair value of stock options granted	$ 2.04	$ 2.98	$ 2.90
Stock options exercised	490,912	890,341	386,356
Total intrinsic value of options exercised	$ 2,100,295	$ 3,266,301	$ 1,163,699
Fair value of grants vested	1,625,742	$ 1,442,478	1,447,612
Unrecognized compensation cost related to unvested stock option	$ 2,900,000			$ 2,900,000
Weighted average period for Unrecognized compensation cost	1 year 6 months 11 days
Cost of common stock repurchased	$ 1,100,000		$ 759,000
Director | Initial Allocation
Stock Based Compensation And Stockholders Equity [Line Items]
Options available for grant	5,000			5,000
Director | Quarterly Option Amount
Stock Based Compensation And Stockholders Equity [Line Items]
Options available for grant	3,000			3,000
2001 Option Plan
Stock Based Compensation And Stockholders Equity [Line Items]
Stock option plan effective date	Sep. 01, 2000
2011 Option Plan
Stock Based Compensation And Stockholders Equity [Line Items]
Stock option plan effective date	May 17, 2010
Options available for grant	711,843			711,843
Options exercisable period, maximum	6 years
Shares options authorized for issuance	3,700,000			3,700,000
2011 Option Plan | Scenario, Plan
Stock Based Compensation And Stockholders Equity [Line Items]
Shares options authorized for issuance	5,000,000			5,000,000
2011 Option Plan | Non Qualified
Stock Based Compensation And Stockholders Equity [Line Items]
Incentive and nonqualified options exercisable	1,203,369	1,071,812	1,893,887	1,203,369
1997 Stock Plan
Stock Based Compensation And Stockholders Equity [Line Items]
Stock option plan effective date	Jul. 09, 2009
Class A Common Shares
Stock Based Compensation And Stockholders Equity [Line Items]
Percentage of board of directors entitled to elect	25.00%
Ownership compared to both classes of common stock	10.00%			10.00%
Common stock dividends declared	$ 0.05
Common stock shares repurchased	4,568,297
Cost of common stock repurchased	$ 25,400,000
Class A Common Shares | Shares Stock Repurchase Plan, August 19, 2002
Stock Based Compensation And Stockholders Equity [Line Items]
Approved number of shares to be repurchased	2,000,000			2,000,000
Common stock shares repurchased	123,482			1,033,344
Cost of common stock repurchased	$ 1,100,000			$ 6,000,000
Shareholder Holding More Than 10% of Outstanding Shares | 2011 Option Plan
Stock Based Compensation And Stockholders Equity [Line Items]
Ownership compared to both classes of common stock	10.00%			10.00%
Options exercisable period, maximum	5 years