Fair Value Disclosures - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 32,914	$ 39,933
Short-term Investments, Gross Unrealized Holding Gains	0	0
Short-term Investments, Gross Unrealized Holding Losses	(7)	(15)
Short-term Investments, Fair Value	$ 32,907	$ 39,918
Available-for-sale securities, maturity period	1 year	1 year
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 32,914	$ 39,933
Short-term Investments, Gross Unrealized Holding Gains	0	0
Short-term Investments, Gross Unrealized Holding Losses	(7)	(15)
Short-term Investments, Fair Value	$ 32,907	$ 39,918