Fair Value of Financial Instruments (Details) - USD ($) | 9 Months Ended | | |
Sep. 30, 2015 | Jun. 30, 2015 | Dec. 31, 2014 |
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 | 16,448,000 | | $ 22,615,000 |
AFS Securities, Fair Value Disclosure | 99,603,000 | | 93,646,000 |
Fair Value, Measurements, Recurring | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
Total assets measured at fair value | 107,918,000 | | 107,459,000 |
Fair Value, Measurements, Recurring | Level 1 | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
Total assets measured at fair value | 8,315,000 | | 7,795,000 |
Fair Value, Measurements, Recurring | Level 2 | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
Total assets measured at fair value | 99,603,000 | | 99,664,000 |
Fair Value, Measurements, Recurring | Money market funds | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
Cash and Cash Equivalents, Fair Value Disclosure | 8,315,000 | | 7,795,000 |
Fair Value, Measurements, Recurring | Money market funds | Level 1 | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
Cash and Cash Equivalents, Fair Value Disclosure | 8,315,000 | | 7,795,000 |
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 | 0 | | 3,225,000 |
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 | | | 3,225,000 |
Fair Value, Measurements, Recurring | U.S. government agency securities | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | $ 13,066,000 | | 5,955,000 |
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 | 13,066,000 | | 5,955,000 |
Fair Value, Measurements, Recurring | U.S. Treasury securities | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | 3,521,000 | | 4,043,000 |
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 | 3,521,000 | | 4,043,000 |
Fair Value, Measurements, Recurring | Municipal debt securities | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | 0 | | 3,924,000 |
Fair Value, Measurements, Recurring | Municipal debt securities | Level 1 | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | $ 0 | | 0 |
Fair Value, Measurements, Recurring | Municipal debt securities | Level 2 | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | | | 3,924,000 |
Fair Value, Measurements, Recurring | Corporate debt securities | | | |
Assets, Fair Value Disclosure [Abstract] | | | |
AFS Securities, Fair Value Disclosure | $ 83,016,000 | | 82,517,000 |
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 | $ 83,016,000 | | $ 82,517,000 |