Valuation and Qualifying Accounts (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning Of Period	$ 7,700	$ 6,580	$ 5,795
Valuation Allowances and Reserves, Charged to Cost and Expense	4,860	4,156	3,063
Deductions	5,573	3,036	2,278
Balance at End of Period	$ 6,987	$ 7,700	$ 6,580