Fair Value of Financial Assets and Liabilities - Derivative Instruments (Change in Fair Value of Warrant and Derivative Liabilities) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)
Derivatives And Fair Value [Line Items]
Balance, Series B Redeemable Preferred Stock	$ 1,493,000
Dilutive Financing Derivative Liability [Member]
Derivatives And Fair Value [Line Items]
Balance, derivative liability
Creation of derivative or warrant liability	2,282,000
Changes in estimated fair value	(611,000)
Payout from liability	(1,545,000)
Balance, derivative liability	126,000
November 2016 Warrant Derivative Liability [Member]
Derivatives And Fair Value [Line Items]
Balance, warrant liability
Creation of derivative or warrant liability	2,929,000
Changes in estimated fair value	(886,000)
Balance, warrant liability	2,043,000
2011 Warrants [Member]
Derivatives And Fair Value [Line Items]
Balance, warrant liability	6,000
Creation of derivative or warrant liability
Changes in estimated fair value	(6,000)
Balance, warrant liability
June 2016 Offering Warrants [Member]
Derivatives And Fair Value [Line Items]
Balance, warrant liability
Creation of derivative or warrant liability	1,816,000
Changes in estimated fair value	(1,542,000)
Balance, warrant liability	274,000
Series B redeemable convertible preferred stock [Member]
Derivatives And Fair Value [Line Items]
Balance, Series B Redeemable Preferred Stock	1,493,000
Changes in estimated fair value	$ (1,493,000)