Fair Value of Financial Assets and Liabilities - Derivative Instruments (Change in Fair Value of Series B Convertible Stock) (Details)	9 Months Ended
	Sep. 30, 2015 USD ($)
Derivatives And Fair Value [Line Items]
Balance, Warrant Liability	$ 5,826,000
Balance, Series B Redeemable Preferred Stock	12,320,000
Balance, Warrant Liability	10,000
Balance, Series B Redeemable Preferred Stock	2,127,000
Series B redeemable convertible preferred stock [Member]
Derivatives And Fair Value [Line Items]
Balance, Series B Redeemable Preferred Stock	12,320,000
Conversions to common stock	(1,496,000)
Changes in estimated fair value	(8,697,000)
Balance, Series B Redeemable Preferred Stock	2,127,000
Warrant Liability [Member]
Derivatives And Fair Value [Line Items]
Balance, Warrant Liability	5,826,000
Issuance	4,210,000
Exercises	(676,000)
Warrants reclassified from liabilities to equity due to amendment of warrants	(5,462,000)
Warrants reclassified from liabilities to equity due to increase in authorized shares	(3,281,000)
Changes in estimated fair value	(607,000)
Balance, Warrant Liability	$ 10,000