Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Assets:
Marketable securities	$ 66,246	$ 82,187
Transfers from Level 1 to Level 2	0	0
Transfers from Level 2 to Level 1	0	0
Transfers into or out of Level 3	0	0
Recurring
Assets:
Cash equivalents	12,779	9,060
Marketable securities	66,246	82,187
Total assets measured at fair value	79,025	91,247
Recurring | Level 1
Assets:
Cash equivalents	11,378	8,810
Total assets measured at fair value	11,378	8,810
Recurring | Level 2
Assets:
Cash equivalents	1,401	250
Marketable securities	66,246	82,187
Total assets measured at fair value	$ 67,647	$ 82,437