Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2014		Apr. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			$ 43,835
Gross Unrealized Gains			94
Gross Unrealized Losses			(14)	[1]
Estimated Fair Value	14,297	[2]	43,915	[2]
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,262		42,033
Gross Unrealized Gains	35		92
Gross Unrealized Losses			(14)	[1]
Estimated Fair Value	14,297	[2]	42,111	[2]
U.S. Treasury And Agency Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			1,802
Gross Unrealized Gains			2
Estimated Fair Value			$ 1,804	[2]

[1] There are no marketable securities that have been in a continuous unrealized loss position for 12 months or more.

[2] The Company's financial assets measured at fair value on a recurring basis include trading securities classified as Level 1 and available-for-sale securities classified as Level 2. As of January 31, 2014 and April 30, 2013, the Company had cash equivalents of $129.2 million and $93.6 million, respectively, classified as Level 1. As of April 30, 2013, the Company had restricted cash of $2.9 million, classified as Level 1. As of January 31, 2014, the Company had no restricted cash balance. As of January 31, 2014 and April 30, 2013, the Company had no investments classified as Level 3.