Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 156,906	$ 210,439
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(19)	(95)
Cash, cash equivalents and short-term investments, Fair market value	156,887	210,344
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	69,538	73,551
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	69,538	73,551
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	87,368	136,888
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(19)	(95)
Cash, cash equivalents and short-term investments, Fair market value	87,349	136,793
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	67,163	73,551
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Fair market value	67,163	73,551
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	13,372	2,997
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(3)
Cash, cash equivalents and short-term investments, Fair market value	13,369	2,997
Government And Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	47,954	75,289
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(2)	(39)
Cash, cash equivalents and short-term investments, Fair market value	47,952	75,250
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	28,417	58,602
Cash, cash equivalents and short-term investments, Gross unrealized gains	0	0
Cash, cash equivalents and short-term investments, Gross unrealized losses	(14)	(56)
Cash, cash equivalents and short-term investments, Fair market value	$ 28,403	$ 58,546