Fair Value of Financial Instruments (Details) - USD ($) | 3 Months Ended | |
Mar. 31, 2017 | Dec. 31, 2016 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount | $ 0 | |
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount | 0 | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 | |
Assets, Fair Value Disclosure [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 43,084,000 | $ 35,033,000 |
AFS Securities, Fair Value Disclosure | 28,250,000 | 39,033,000 |
Fair Value, Measurements, Recurring | | |
Assets, Fair Value Disclosure [Abstract] | | |
Total assets measured at fair value | 45,807,000 | 45,706,000 |
Fair Value, Measurements, Recurring | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
Total assets measured at fair value | 11,909,000 | 4,996,000 |
Fair Value, Measurements, Recurring | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
Total assets measured at fair value | 33,898,000 | 40,710,000 |
Fair Value, Measurements, Recurring | Money market funds | | |
Assets, Fair Value Disclosure [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 11,909,000 | 4,996,000 |
Fair Value, Measurements, Recurring | Money market funds | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 11,909,000 | 4,996,000 |
Fair Value, Measurements, Recurring | Money market funds | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Fair Value, Measurements, Recurring | Commercial paper | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 2,082,000 | 1,322,000 |
Fair Value, Measurements, Recurring | Commercial paper | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 0 | 0 |
Fair Value, Measurements, Recurring | Commercial paper | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 2,082,000 | 1,322,000 |
Fair Value, Measurements, Recurring | U.S. government agency securities | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 3,282,000 | 4,177,000 |
Fair Value, Measurements, Recurring | U.S. government agency securities | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. government agency securities | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 3,282,000 | 4,177,000 |
Fair Value, Measurements, Recurring | U.S. Treasury securities | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 1,300,000 | 2,045,000 |
Fair Value, Measurements, Recurring | U.S. Treasury securities | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 0 | 0 |
Fair Value, Measurements, Recurring | U.S. Treasury securities | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 1,300,000 | 2,045,000 |
Fair Value, Measurements, Recurring | Corporate debt securities | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 27,234,000 | 33,166,000 |
Fair Value, Measurements, Recurring | Corporate debt securities | Level 1 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | 0 | 0 |
Fair Value, Measurements, Recurring | Corporate debt securities | Level 2 | | |
Assets, Fair Value Disclosure [Abstract] | | |
AFS Securities, Fair Value Disclosure | $ 27,234,000 | $ 33,166,000 |