Short-Term Borrowings - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended											12 Months Ended				12 Months Ended
	Apr. 30, 2011	Jan. 31, 2011	Jan. 31, 2012	Apr. 30, 2011 Minimum	Jan. 31, 2012 Minimum	Apr. 30, 2011 Maximum	Jan. 31, 2012 Maximum	Jan. 31, 2012 Covenant Requirement	Jan. 31, 2012 Line of Credit	Jan. 31, 2012 Line of Credit Federal Funds Rate	Jan. 31, 2012 Line of Credit One Month LIBOR	Jan. 31, 2012 Line of Credit Minimum	Jan. 31, 2012 Line of Credit Minimum LIBOR	Jan. 31, 2012 Line of Credit Minimum Base Rate	Jan. 31, 2012 Line of Credit Maximum	Jan. 31, 2012 Line of Credit Maximum LIBOR	Jan. 31, 2012 Line of Credit Maximum Base Rate	Jan. 31, 2012 Amended Line of Credit Facility	Jan. 31, 2012 Amended Line of Credit Facility Minimum	Jan. 31, 2012 Amended Line of Credit Facility Minimum LIBOR	Jan. 31, 2012 Amended Line of Credit Facility Minimum Base Rate	Jan. 31, 2012 Amended Line of Credit Facility Maximum	Jan. 31, 2012 Amended Line of Credit Facility Maximum LIBOR	Jan. 31, 2012 Amended Line of Credit Facility Maximum Base Rate
Short-term Debt [Line Items]
Termination date for senior, unsecured revolving credit facility	2015-04-27
Revolving credit facility, maximum borrowing capacity	$ 125,000		$ 125,000															$ 100,000
Description of interest payment option									We have the option to pay interest based on: (i) London Interbank Offered Rate (LIBOR) with varying maturities commensurate with the borrowing period we select, plus a spread of between 2.25% and 3.25% based on a pricing grid tied to a financial covenant, or (ii) A base rate plus a spread of between 1.25% and 2.25%, based on a pricing grid tied to a financial covenant.									(i) LIBOR with varying maturities commensurate with the borrowing period we select, plus a spread of between 1.0% and 1.6%, based on a pricing grid tied to a financial covenant, or (ii) A base rate plus a spread of between 0.0% and 0.6%, based on a pricing grid tied to a financial covenant.
Debt instrument, basis spread on variable rate										0.50%	1.00%		2.25%	1.25%		3.25%	2.25%			1.00%	0.00%		1.60%	0.60%
Commitment fee on unused revolving credit facility				0.40%	0.40%	0.50%	0.50%												0.25%			0.35%
Revolving credit facility financial and other covenants									This revolving credit facility contains certain financial and other covenants, including the following: • Our adjusted quick ratio (ratio of the sum of cash and cash equivalents, short-term investments, and net current receivables to total current liabilities) shall not be less than 1.00; • Our tangible net worth (stockholders’ equity less goodwill and other intangible assets) must exceed the calculated required tangible net worth as defined in the credit agreement, which establishes a fixed level of required tangible net worth. Each quarter the required level increases by 70% of any positive net income in the quarter (but in the aggregate no more than 70% of positive net income for any full fiscal year), 100% of the amortization of intangible assets in the quarter, and100% of certain stock issuance proceeds. The required level also decreases each quarter by 50% of amounts paid for dividends or repurchases of our stock and certain amounts of acquired intangible assets; • Our leverage ratio (ratio of total liabilities less subordinated debt to the sum of subordinated debt and tangible net worth) shall be less than 2.00; • Our senior leverage ratio (ratio of total debt less subordinated debt to the sum of subordinated debt and tangible net worth) shall not be greater than 0.90; and • Our minimum cash and accounts receivable ratio (ratio of the sum of cash and cash equivalents, short-term investments, and 42.0% of net current accounts receivable, to outstanding credit agreement borrowings) shall not be less than 1.25.
Adjusted quick ratio, lower limit												1
Leverage ratio, upper limit															2
Senior leverage ratio, upper limit															0.90
Percentage of net current account receivable ratio included in cash and account receivable ratio									42.00%
Cash and accounts receivable ratio, lower limit												1.25
Revolving credit facility terms of covenants								The revolving credit facility limits the aggregate amount we can pay for dividends and repurchases of our stock over the four year term of the facility to $50,000 plus 70% of our cumulative net income.
Credit facility limits, aggregate amount available for dividend and repurchase of stock								50,000
Credit facility limits, aggregate amount available for dividend and repurchase of stock, percentage of cumulative net income								70.00%
Borrowing from revolving credit facility		60,000
Repayment of revolving credit facility		$ 80,000