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 |