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Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Dec. 31, 2011
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Corporate bonds $ 30,126 $ 29,776 $ 30,923
Level 1 [Member]
     
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Deferred compensation plan assets 47,922 39,779  
Corporate bonds 30,126 29,776  
Level 2 [Member]
     
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Interest rate swap (539) (817)  
Level 3 [Member]
     
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Contingent purchase price liabilities $ (30,861) $ (30,012)