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Cash Equivalents and Investments - Schedule of Investments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2015
Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]    
Short-Term $ 8,021 $ 6,035
Long-Term 59,270 64,082
Municipal Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Short-Term 7,773 5,539
Long-Term 35,089 35,827
Federal Home Loan Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Long-Term 22,221 27,030
Certificates of Deposit [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Short-Term 248 496
Long-Term $ 1,960 $ 1,225