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Financial Instruments - Additional Information (Detail) (USD $)
 3 Months Ended
Mar. 31, 2013
Y
Mar. 31, 2012
Dec. 31, 2012
Investment Securities [Line Items]      
Cash and cash equivalents of not-for-profit schools with restrictions $ 79,800,000   $ 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 (1,000) 12,000  
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    
Number of days for termination notice 5 days    
Loans disbursed under Credit Agreement secured by cash, percentage 110.00%    
Repayment of amount borrowed 80,000,000    
Credit Agreement [Member]
      
Investment Securities [Line Items]      
Minimum cash under covenant term 75,000,000    
Municipal bond [Member]
      
Investment Securities [Line Items]      
Period debt obligations mature, years, maximum 1 year    
Cumulative unrealized losses on municipal bonds $ 500,000