Fair Value Measurements - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Cash and cash equivalents
Cash	$ 12,669,000	$ 15,129,000
Money market funds	62,279,000	62,278,000
Total cash and cash equivalents	74,948,000	77,407,000	68,669,000	77,376,000
Long-term investments
U.S. Treasury Bills	2,600,000	2,599,000
Total cash and cash equivalents and investments	77,548,000	80,006,000
Fair Value, Inputs, Level 1
Long-term investments
Cash and cash equivalents	74,900,000
Long-term restricted cash	$ 2,600,000