Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Redeemable Convertible Preferred Stock Series B [Member]
Preferred stock, par or stated value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock liquidation preference value (in dollars per share)	$ 1,000	$ 1,000
Preferred stock shares authorized (in shares)	35,000	35,000
Preferred stock shares issued (in shares)	30,700	30,700	35,000
Preferred stock shares outstanding (in shares)	30,700	30,700
Common Class A [Member]
Common stock, par or stated value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock shares issued (in shares)	17,667,857	17,667,857
Common stock shares outstanding (in shares)	17,667,857	17,667,857