Cash Equivalents and Investments - Schedule of Securities Classified as Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016 | Mar. 31, 2016 | Dec. 31, 2015 |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Cash and cash equivalents, Amortized Cost | $ 71,213 | $ 74,598 | [1] | $ 171,678 | $ 107,004 |
Cash and cash equivalents, Gross Unrealized Gains | 0 | 0 | | | |
Cash and cash equivalents, Gross Unrealized Losses | 0 | 0 | | | |
Cash and cash equivalents, Fair Value | 71,213 | 74,598 | | | |
Short-term investments, Amortized Cost | 102,258 | 126,296 | | | |
Short-term investments, Gross Unrealized Gains | 5 | 7 | | | |
Short-term investments, Gross Unrealized Losses | (53) | (78) | | | |
Short-term investments, Fair Value | 102,210 | 126,225 | | | |
Cash equivalents and short-term investments, Amortized Cost | 173,471 | 200,894 | | | |
Cash equivalents and short-term investments, Gross Unrealized Gains | 5 | 7 | | | |
Cash equivalents and short-term investments, Gross Unrealized Losses | (53) | (78) | | | |
Cash equivalents and short-term investments, Fair Value | 173,423 | 200,823 | | | |
Cash [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Cash and cash equivalents, Amortized Cost | 1,084 | 3,638 | | | |
Cash and cash equivalents, Gross Unrealized Gains | 0 | 0 | | | |
Cash and cash equivalents, Gross Unrealized Losses | 0 | 0 | | | |
Cash and cash equivalents, Fair Value | 1,084 | 3,638 | | | |
Money Market Funds [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Cash and cash equivalents, Amortized Cost | 70,129 | 68,561 | | | |
Cash and cash equivalents, Gross Unrealized Gains | 0 | 0 | | | |
Cash and cash equivalents, Gross Unrealized Losses | 0 | 0 | | | |
Cash and cash equivalents, Fair Value | 70,129 | 68,561 | | | |
Commercial Paper (Cash Equivalents) [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Cash and cash equivalents, Amortized Cost | | 2,399 | | | |
Cash and cash equivalents, Gross Unrealized Gains | | 0 | | | |
Cash and cash equivalents, Gross Unrealized Losses | | 0 | | | |
Cash and cash equivalents, Fair Value | | 2,399 | | | |
Corporate Bonds (Investments) [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Short-term investments, Amortized Cost | 46,098 | 58,464 | | | |
Short-term investments, Gross Unrealized Gains | 2 | 2 | | | |
Short-term investments, Gross Unrealized Losses | (33) | (56) | | | |
Short-term investments, Fair Value | 46,067 | 58,410 | | | |
Commercial Paper (Investments) [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Short-term investments, Amortized Cost | 41,792 | 62,946 | | | |
Short-term investments, Gross Unrealized Gains | 2 | 5 | | | |
Short-term investments, Gross Unrealized Losses | (7) | (20) | | | |
Short-term investments, Fair Value | 41,787 | 62,931 | | | |
Asset-Backed Securities [Member] | | | | | |
Cash Cash Equivalents And Short Term Investments [Line Items] | | | | | |
Short-term investments, Amortized Cost | 14,368 | 4,886 | | | |
Short-term investments, Gross Unrealized Gains | 1 | | | | |
Short-term investments, Gross Unrealized Losses | (13) | (2) | | | |
Short-term investments, Fair Value | $ 14,356 | $ 4,884 | | | |
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[1] | Derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2016. |