Summary of Significant Accounting Policies - Stock option equivalents (Details) - shares shares in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	426	361	404
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	0	13	34
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	193	133	133
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)	196	73	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)	0	3	21
Restricted stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of common stock equivalents outstanding (in shares)	37	139	216