Fair Value Measurements - Additional Information (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Cash and cash equivalents
Cash	$ 17,117,000	$ 28,436,000
Money market funds	62,241,000	62,261,000
Total cash and cash equivalents	79,358,000	90,697,000	82,833,000	77,407,000
Long-term restricted cash and investments
Restricted cash	525,000	0
U.S. Treasury Bills	2,599,000	2,599,000
Total cash and cash equivalents, restricted cash and investments	82,482,000	93,296,000
Fair Value, Inputs, Level 1
Long-term restricted cash and investments
Restricted cash	3,100,000
Cash and cash equivalents, fair value disclosure	$ 79,400,000