Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 236,072	$ 256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	1
Cash, cash equivalents and short-term investments, Gross unrealized losses	(56)
Cash, cash equivalents and short-term investments, Fair market value	236,017	256,965
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	52,299	256,965
Cash, cash equivalents and short-term investments, Fair market value	52,299	256,965
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	183,773
Cash, cash equivalents and short-term investments, Gross unrealized gains	1
Cash, cash equivalents and short-term investments, Gross unrealized losses	(56)
Cash, cash equivalents and short-term investments, Fair market value	183,718
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	52,299	256,965
Cash, cash equivalents and short-term investments, Fair market value	52,299	256,965
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	2,995
Cash, cash equivalents and short-term investments, Fair market value	2,995
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	92,846
Cash, cash equivalents and short-term investments, Gross unrealized gains	1
Cash, cash equivalents and short-term investments, Gross unrealized losses	(25)
Cash, cash equivalents and short-term investments, Fair market value	92,822
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	87,932
Cash, cash equivalents and short-term investments, Gross unrealized losses	(31)
Cash, cash equivalents and short-term investments, Fair market value	$ 87,901