Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Cash and cash equivalents
Cash	$ 31,582	$ 27,186
Restricted cash	0	525
Money market funds	54,736	62,244
Total cash and cash equivalents	86,318	89,955	$ 85,683	$ 90,697
Long-term investments
Long-term restricted cash	2,599	2,600
Total cash and cash equivalents and investments	88,917	$ 92,555
Increase (decrease) in restricted cash	(500)
Fair Value, Inputs, Level 1
Long-term investments
Cash and cash equivalents, at fair value	86,300
Restricted cash, at fair value	$ 2,600