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Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $)
Sep. 30, 2013
Dec. 31, 2012
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost $ 5,903,000 $ 9,870,000
Gross Unrealized Gains (Losses) (27,000) 29,000
Recorded Basis 5,876,000 9,899,000
Recorded Basis 7,108,000 16,748,000
Held-to-maturity [Member] | Corporate bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Held-to-maturity, Cost 0 467,000
Held-to-maturity, Gross Unrealized Gains (Losses) 0 0
Held-to-maturity, Recorded Basis 0 467,000
Fair Value Category   2
Long-term Available-for-Sale [Member] | Corporate bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 1,613,000 9,111,000
Gross Unrealized Gains (Losses) (15,000) 28,000
Recorded Basis 1,598,000 9,139,000
Fair Value Category   2
Long-term Available-for-Sale [Member] | Municipal bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 4,290,000 292,000
Gross Unrealized Gains (Losses) (12,000) 1,000
Recorded Basis 4,278,000 293,000
Fair Value Category   2
Current Available-for-Sale [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 7,121,000 16,728,000
Gross Unrealized Gains (Losses) (13,000) 20,000
Recorded Basis 7,108,000 16,748,000
Current Available-for-Sale [Member] | Corporate bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 256,000 14,764,000
Gross Unrealized Gains (Losses) (4,000) 16,000
Recorded Basis 252,000 14,780,000
Fair Value Category   2
Current Available-for-Sale [Member] | Municipal bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 5,000 409,000
Gross Unrealized Gains (Losses) 0 1,000
Recorded Basis 5,000 410,000
Fair Value Category   2
Current Available-for-Sale [Member] | Certificate of deposits [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 6,860,000 0
Gross Unrealized Gains (Losses) (9,000) 0
Recorded Basis 6,851,000 0
Fair Value Category   2
Current Available-for-Sale [Member] | U.S. treasuries [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 0 1,555,000
Gross Unrealized Gains (Losses) 0 3,000
Recorded Basis $ 0 $ 1,558,000
Fair Value Category   1