Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 129,161	$ 192,602
Cash, cash equivalents and short-term investments, Gross unrealized gains	3
Cash, cash equivalents and short-term investments, Gross unrealized losses	(8)	(111)
Cash, cash equivalents and short-term investments, Fair market value	129,156	192,491
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	38,001	80,304
Cash, cash equivalents and short-term investments, Fair market value	38,001	80,304
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	91,160	112,298
Cash, cash equivalents and short-term investments, Gross unrealized gains	3
Cash, cash equivalents and short-term investments, Gross unrealized losses	(8)	(111)
Cash, cash equivalents and short-term investments, Fair market value	91,155	112,187
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	38,001	75,304
Cash, cash equivalents and short-term investments, Fair market value	38,001	75,304
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	29,972	48,936
Cash, cash equivalents and short-term investments, Gross unrealized losses	(1)	(37)
Cash, cash equivalents and short-term investments, Fair market value	29,971	48,899
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	43,826	50,966
Cash, cash equivalents and short-term investments, Gross unrealized gains	3
Cash, cash equivalents and short-term investments, Gross unrealized losses	(1)	(48)
Cash, cash equivalents and short-term investments, Fair market value	43,828	50,918
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	17,362	17,396
Cash, cash equivalents and short-term investments, Gross unrealized losses	(6)	(26)
Cash, cash equivalents and short-term investments, Fair market value	$ 17,356	$ 17,370