Fair Value of Financial Instruments (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Assets, fair value	$ 93,282	$ 26,163
Quotes Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, fair value	75,191	556
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value	18,091	25,607
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value	0	0
Money market funds (cash equivalents) [Member]
Assets:
Assets, fair value	75,191	556
Money market funds (cash equivalents) [Member] | Quotes Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, fair value	75,191	556
Money market funds (cash equivalents) [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value	0	0
Money market funds (cash equivalents) [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value	0	0
Corporate notes and bonds [Member]
Assets:
Assets, fair value	16,591	18,821
Corporate notes and bonds [Member] | Quotes Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, fair value	0	0
Corporate notes and bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value	16,591	18,821
Corporate notes and bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value	0	0
U.S. government and agency securities [Member]
Assets:
Assets, fair value	1,500	3,503
U.S. government and agency securities [Member] | Quotes Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, fair value	0	0
U.S. government and agency securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value	1,500	3,503
U.S. government and agency securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value	0	0
Commercial paper [Member]
Assets:
Assets, fair value	0	3,283
Commercial paper [Member] | Quotes Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets, fair value	0	0
Commercial paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, fair value	0	3,283
Commercial paper [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, fair value	$ 0	$ 0