Fair Value Measurement of Assets on Recurring Basis (Detail) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds	$ 13,144	$ 13,536	$ 12,816
Equities	8,427	7,057	5,746
Total	21,571	20,593	18,562
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common/collective trust funds	2,229	2,192	1,965
Total	$ 2,229	$ 2,192	$ 1,965