Fair Value Measurements - Additional Information (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash and cash equivalents
Cash	$ 15,129,000	$ 10,087,000
Money market funds	62,278,000	67,289,000
Total cash and cash equivalents	77,407,000	77,376,000	139,586,000	94,993,000
Long-term investments
U.S. Treasury Bills	2,599,000	2,599,000
Total cash and cash equivalents and investments	80,006,000	79,975,000
Fair Value, Inputs, Level 1
Long-term investments
Cash and cash equivalents	77,400,000
Long-term restricted cash	$ 2,600,000