Fair Value - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Assets measured at fair value
Cash and cash equivalents	$ 44,344	$ 10,014	$ 23,829	$ 8,896
Restricted cash	250	375
Short term investments		6,191
Total	44,594	16,580
Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Cash and cash equivalents	44,344	10,014
Restricted cash	250	375
Total	44,594	10,389
Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Short term investments		6,191
Total		$ 6,191