Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (Fair value measurement on recurring basis, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	$ 16,415	$ 13,892
Total assets measured at fair value	16,415	13,892
Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	16,415	13,892
Total assets measured at fair value	16,415	13,892
Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	0	0
Total assets measured at fair value	0	0
Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	0	0
Total assets measured at fair value	$ 0	$ 0