Summary of Company Cash , Cash Equivalents and Short-term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	$ 279,574	$ 256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	9
Cash, cash equivalents and short-term investments, Gross unrealized losses	(44)
Cash, cash equivalents and short-term investments, Fair market value	279,539	256,965
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	102,754	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains
Cash, cash equivalents and short-term investments, Gross unrealized losses
Cash, cash equivalents and short-term investments, Fair market value	102,754	256,965
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	176,820
Cash, cash equivalents and short-term investments, Gross unrealized gains	9
Cash, cash equivalents and short-term investments, Gross unrealized losses	(44)
Cash, cash equivalents and short-term investments, Fair market value	176,785
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	95,504	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains
Cash, cash equivalents and short-term investments, Gross unrealized losses
Cash, cash equivalents and short-term investments, Fair market value	95,504	256,965
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	20,649
Cash, cash equivalents and short-term investments, Gross unrealized gains	1
Cash, cash equivalents and short-term investments, Gross unrealized losses
Cash, cash equivalents and short-term investments, Fair market value	20,650
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	92,198
Cash, cash equivalents and short-term investments, Gross unrealized gains	3
Cash, cash equivalents and short-term investments, Gross unrealized losses	(23)
Cash, cash equivalents and short-term investments, Fair market value	92,178
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost	71,223
Cash, cash equivalents and short-term investments, Gross unrealized gains	5
Cash, cash equivalents and short-term investments, Gross unrealized losses	(21)
Cash, cash equivalents and short-term investments, Fair market value	$ 71,207