Summary of Significant Accounting Policies - Stock option equivalents (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	361,000	404,000	1,888,000
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	139,000	216,000	137,000
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	133,000	133,000	133,000
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	73,000	0	0
Option Matching Rights [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	3,000	21,000	229,000
Restricted stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	13,000	34,000	57,000
Shares to be issued upon conversion of convertible of long-term loan, related party [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	0	0	1,332,000