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Financial Instruments - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Y
Jun. 30, 2012
Dec. 31, 2012
Financial Instruments [Line Items]          
Cash and cash equivalents of not-for-profit schools with restrictions $ 72,500,000   $ 72,500,000   $ 87,200,000
Period cash equivalents and short-term investments have been in continuous unrealized loss position, years, maximum     1 year    
Period cash equivalents and long-term investments have been in continuous unrealized loss position, years, minimum     1 year    
Cumulative unrealized losses on municipal bonds (4,000) 108,000 (5,000) 120,000  
Years ARS auction events have been failing     3    
Revolving credit facility maturity date     Jan. 31, 2014    
Number of days for pre-payment notice 3 days   3 days    
Number of days for termination notice 5 days   5 days    
Loans disbursed under Credit Agreement secured by cash, percentage 110.00%   110.00%    
Repayment of amount borrowed     0    
Credit Agreement [Member]
          
Financial Instruments [Line Items]          
Minimum cash under covenant term 75,000,000   75,000,000    
Municipal bond [Member]
          
Financial Instruments [Line Items]          
Period debt obligations mature, years, maximum     1 year    
Cumulative unrealized losses on municipal bonds     $ 500,000