Fair Value Measurements - Common Stock Warrants (Details) - $ / shares	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Historical volatilities period	7 years
Fair value of common stock warrants (in usd per share)	$ 13.04	$ 23.47
Employee Stock Option
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock warrants outstanding (in shares)	354,350	345,135