Financial Instruments - Summary of Investment in Cash Equivalents and Marketable Securities (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 102,244,000
Due within one year	87,235,000
Unrealized Gains	2,000
Due within two years	14,950,000
Unrealized Losses	(61,000)
Fair Value	102,185,000
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	79,717,000
Unrealized Gains		$ 0
Unrealized Losses		$ 0
Fair Value	79,717,000
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,042,000
Unrealized Losses	(34,000)
Fair Value	10,008,000
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,499,000
Unrealized Gains	1,000
Fair Value	2,500,000
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,489,000
Unrealized Losses	(27,000)
Fair Value	7,462,000
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,497,000
Unrealized Gains	1,000
Fair Value	$ 2,498,000