Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies [Line Items]
Percentage of more likely than not likelihood of fair value less than carrying amount	50.00%
Recognized income tax positions largest amount likely of being realized	50.00%
Stock options to purchase common stock	1,603,334	2,043,774	2,020,767
Shares excluded from the computation of the diluted net income per weighted-average common share	874,298	1,116,106	1,179,840
Advertising expense	$ 1.0	$ 1.4	$ 1.0
Equity Method Investments
Summary Of Significant Accounting Policies [Line Items]
Ownership interest	50.00%
Cost Method Investments
Summary Of Significant Accounting Policies [Line Items]
Ownership interest	20.00%