Fair Value Measurement - Assumptions (Details) - USD ($) $ in Thousands		12 Months Ended
	Apr. 20, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from issuance of warrants	$ 2,200	$ 2,200	$ 0
PEAK6
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from issuance of warrants		700
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value		2,840
Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants, fair value		$ 2,840
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Warrant
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility of underlying		50.00%
Risk-free rate		1.78%
Dividend yield		0.00%
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Warrant | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of Designated Event		0.00%
Timing of Designated Event		3 years
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Warrant | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of Designated Event		50.00%
Timing of Designated Event		5 years
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Replacement Warrant
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility of underlying		55.00%
Risk-free rate		2.02%
Dividend yield		0.00%
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Replacement Warrant | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of Designated Event		0.00%
Timing of Designated Event		3 years
Fair Value, Measurements, Nonrecurring | Monte Carlo | Level 3 | Replacement Warrant | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of Designated Event		50.00%
Timing of Designated Event		5 years