Auction Rate Securities - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended
	Oct. 31, 2012 Entity		Apr. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of different issuers the Company held investments in for auction rate securities	4
Investments in auction rate securities	$ 20,000,000
Interest rate revising interval	30 days
Auction rate securities, earliest maturity period	2033
Auction rate securities, latest maturity period	2050
Auction rate securities, redeemed			5,000,000
Investments in auction rate securities, estimated fair value	17,780,000	[1]	12,994,000	[1]
Unrealized losses recorded in accumulated other comprehensive loss, before tax	(200,000)		0
Unrealized losses recorded in accumulated other comprehensive loss, net of taxes	(100,000)		0
Single Issuer Investment
Schedule of Available-for-sale Securities [Line Items]
Investments in auction rate securities	5,000,000
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Auction rate security, at fair value, that was not in unrealized loss position	10,000,000		12,994,000
Auction rate securities, continuous unrealized loss position, less than twelve months, fair value	$ 7,800,000

[1] For investments in auction rate securities, the fair values were based on discounted cash flow valuation models, primarily utilizing unobservable inputs. See Note 6, "Auction Rate Securities," for the roll-forwards of assets measured at fair value using significant unobservable Level 3 inputs and the sensitivity analysis of significant inputs.