Investments and Fair Value Measurements - Investments in Accordance with Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments And Fair Value Measurements [Line Items]
Total Investments	$ 235,235	$ 198,153
Contingent consideration, current and noncurrent	21,052	38,050	8,704
Self-insurance	2,554	1,375	1,640
Liabilities	23,606	39,425
Money Market Funds [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	52,595	112,714
U.S. Government and Sponsored Entities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	28,909	20,177
Corporate Debt Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	117,195	42,069
Municipal Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	17,377	1,713
Asset-Backed Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	14,236	12,192
Mortgage-Backed Securities - Residential [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	4,923	9,288
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	65,307	127,928
Contingent consideration, current and noncurrent
Self-insurance
Liabilities
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	52,595	112,714
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government and Sponsored Entities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	12,712	15,214
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Debt Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Asset-Backed Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage-Backed Securities - Residential [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Significant other Observable Inputs (Level 2) [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	169,827	70,172
Contingent consideration, current and noncurrent
Self-insurance
Liabilities
Significant other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Significant other Observable Inputs (Level 2) [Member] | U.S. Government and Sponsored Entities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	16,197	4,963
Significant other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	117,195	42,069
Significant other Observable Inputs (Level 2) [Member] | Municipal Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	17,377	1,713
Significant other Observable Inputs (Level 2) [Member] | Asset-Backed Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	14,135	12,139
Significant other Observable Inputs (Level 2) [Member] | Mortgage-Backed Securities - Residential [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	4,923	9,288
Unobservable Inputs (Level 3) [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	101	53
Contingent consideration, current and noncurrent	21,052	38,050
Self-insurance	2,554	1,375
Liabilities	23,606	39,425
Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Unobservable Inputs (Level 3) [Member] | U.S. Government and Sponsored Entities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Unobservable Inputs (Level 3) [Member] | Corporate Debt Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Unobservable Inputs (Level 3) [Member] | Municipal Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments
Unobservable Inputs (Level 3) [Member] | Asset-Backed Securities [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments	101	53
Unobservable Inputs (Level 3) [Member] | Mortgage-Backed Securities - Residential [Member]
Investments And Fair Value Measurements [Line Items]
Total Investments