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Fair Value Measurement - Summary of Marketable Securities Consist of Investments (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Recorded Basis $ 6,680 $ 5,909
Recorded Basis 31,013 19,787
Long-Term Available-for-Sale [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 6,747 5,953
Gross Unrealized Losses (67) (44)
Recorded Basis 6,680 5,909
Corporate Bonds [Member] | Long-Term Available-for-Sale [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 2,422 1,879
Gross Unrealized Losses (40) (27)
Recorded Basis 2,382 1,852
Fair Value Category 2  
Municipal Bonds [Member] | Long-Term Available-for-Sale [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 4,325 4,074
Gross Unrealized Losses (27) (17)
Recorded Basis 4,298 4,057
Fair Value Category 2  
Current Available-for-Sale [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 31,028 19,800
Gross Unrealized Losses (15) (13)
Recorded Basis 31,013 19,787
Current Available-for-Sale [Member] | Variable Rate Demand Notes (VRDN) [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 20,000 10,000
Gross Unrealized Losses 0 0
Recorded Basis 20,000 10,000
Fair Value Category 2  
Current Available-for-Sale [Member] | Corporate Bonds [Member]
    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Cost 11,028 9,800
Gross Unrealized Losses (15) (13)
Recorded Basis $ 11,013 $ 9,787
Fair Value Category 2