Significant Accounting Policies, Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	$ 49,392	$ 53,409
Recurring [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	41,738	45,816
Recurring [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	13,600	9,297
Recurring [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	28,138	36,519
Recurring [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Money Market Funds [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	13,600	9,297
Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	13,600	9,297
Recurring [Member] | Money Market Funds [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Money Market Funds [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Certificates of Deposit [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	1,210	1,273
Recurring [Member] | Certificates of Deposit [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Certificates of Deposit [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	1,210	1,273
Recurring [Member] | Certificates of Deposit [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Commercial Paper [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	997	4,989
Recurring [Member] | Commercial Paper [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	997	4,989
Recurring [Member] | Commercial Paper [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Corporate Notes and Bonds [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	20,018	19,317
Recurring [Member] | Corporate Notes and Bonds [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | Corporate Notes and Bonds [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	20,018	19,317
Recurring [Member] | Corporate Notes and Bonds [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | U.S. Government Agency Securities [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	5,913	10,940
Recurring [Member] | U.S. Government Agency Securities [Member] | Level 1 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	0	0
Recurring [Member] | U.S. Government Agency Securities [Member] | Level 2 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	5,913	10,940
Recurring [Member] | U.S. Government Agency Securities [Member] | Level 3 [Member]
Fair value hierarchy for financial assets measured at fair value [Abstract]
Fair value for financial assets	$ 0	$ 0