Assets and Liabilities Measured at Fair Value and Related Hierarchy Levels (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Mar. 31, 2012	Dec. 31, 2011
Fair Value Measurements [Line Items]
Total available-for-sale securities	$ 16,223			$ 17,044
September 2010 interest rate swap arrangement with a base rate of 0.56% and an aggregate notional amount of $150,000				95	[1]
Executive deferred compensation plan trust	2,743	[2]		2,218	[2]
Total fuel price derivatives - assets	428
Total fuel price derivatives - liabilities	2,274
Contingent consideration	991		8,486	9,325
Mortgage-backed securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	2,153			3,197
Asset-backed securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	1,709			1,930
Municipal bonds
Fair Value Measurements [Line Items]
Total available-for-sale securities	143			149
Equity securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	12,218			11,768
Fuel price derivatives - diesel
Fair Value Measurements [Line Items]
Total fuel price derivatives - assets	110	[3]
Total fuel price derivatives - liabilities	524	[3]		25	[3]
Fuel price derivatives - unleaded fuel
Fair Value Measurements [Line Items]
Total fuel price derivatives - assets	318	[3]		20	[3]
Total fuel price derivatives - liabilities	1,750	[3]
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements [Line Items]
Total available-for-sale securities	12,218			11,768
Executive deferred compensation plan trust	2,743	[2]		2,218	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	12,218			11,768
Significant Other Observable Inputs (Level 2)
Fair Value Measurements [Line Items]
Total available-for-sale securities	4,005			5,276
September 2010 interest rate swap arrangement with a base rate of 0.56% and an aggregate notional amount of $150,000				95	[1]
Total fuel price derivatives - assets	318
Total fuel price derivatives - liabilities	1,750
Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	2,153			3,197
Significant Other Observable Inputs (Level 2) | Asset-backed securities
Fair Value Measurements [Line Items]
Total available-for-sale securities	1,709			1,930
Significant Other Observable Inputs (Level 2) | Municipal bonds
Fair Value Measurements [Line Items]
Total available-for-sale securities	143			149
Significant Other Observable Inputs (Level 2) | Fuel price derivatives - unleaded fuel
Fair Value Measurements [Line Items]
Total fuel price derivatives - assets	318	[3]		20	[3]
Total fuel price derivatives - liabilities	1,750	[3]
Significant Other Observable Inputs (Level 3)
Fair Value Measurements [Line Items]
Total fuel price derivatives - assets	110
Total fuel price derivatives - liabilities	524
Contingent consideration	991			9,325
Significant Other Observable Inputs (Level 3) | Fuel price derivatives - diesel
Fair Value Measurements [Line Items]
Total fuel price derivatives - assets	110	[3]
Total fuel price derivatives - liabilities	$ 524	[3]		$ 25	[3]

[1] The fair value of these instruments is recorded in accrued expenses.

[2] The fair value of these instruments is recorded in other assets.

[3] The balance sheet presentation combines unleaded fuel and diesel fuel positions.