Stockholders' Equity (Details Textual)			6 Months Ended	12 Months Ended
	Jul. 07, 2015 $ / shares shares	Jun. 16, 2015	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) vote $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 shares
Common stock
Issuance of common stock - IPO	10,350,000			10,350,000
Public offering share price (in dollars per share) | $ / shares	$ 15.00
Common stock, shares authorized	200,000,000			200,000,000	80,000,000
Common stock dividends declared to date | $				$ 0
Number of votes per share of common stock | vote				1
Common stock, shares outstanding, beginning balance (in shares)			4,286,164	4,286,164	4,161,178
Issuance of common stock - option & warrant exercises				395,192	124,986
Issuance of restricted common stock				174,530
Issuance of common stock - preferred stock conversion to common stock				2,590,241
Common stock, shares outstanding, ending balance (in shares)				41,110,127	4,286,164	4,161,178
Preferred stock
Preferred stock, par value | $ / shares				$ 0.00001	$ 0.00001
Preferred stock, shares authorized	5,000,000			5,000,000	0
Convertible preferred stock, shares authorized				0	53,496,241
Convertible preferred stock, shares issued				0	50,985,652
Convertible preferred stock aggregate liquidation value | $				$ 0	$ 352,626,000
Convertible preferred stock, shares outstanding				0	50,985,652
Basis for conversion of preferred stock into common stock			0.5
Public offering proceeds that would trigger conversion of preferred stock | $			$ 50,000,000.0
Offering price that would trigger conversion of preferred stock (in dollars per share) | $ / shares			$ 20.00
Threshold ownership of capital stock to trigger requirement for preferred stockholders vote on related actions (as a percent)			10.00%
Threshold ownership of preferred stock for right of first refusal (in shares)			300,000
Series A convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					3,410,278
Convertible preferred stock, shares issued					3,410,278
Convertible preferred stock aggregate liquidation value | $					$ 3,410,000
Convertible preferred stock, shares outstanding					3,410,278
Dividend rate (in dollars per share) | $ / shares			$ 0.10
Liquidation preference (in dollars per share) | $ / shares			1.00
Series B convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					4,469,349
Convertible preferred stock, shares issued					4,469,349
Convertible preferred stock aggregate liquidation value | $					$ 12,023,000
Convertible preferred stock, shares outstanding					4,469,349
Dividend rate (in dollars per share) | $ / shares			0.27
Liquidation preference (in dollars per share) | $ / shares			2.69
Series C convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					5,191,754
Convertible preferred stock, shares issued					4,906,040
Convertible preferred stock aggregate liquidation value | $					$ 17,171,000
Convertible preferred stock, shares outstanding					4,906,040
Dividend rate (in dollars per share) | $ / shares			0.35
Liquidation preference (in dollars per share) | $ / shares			3.50
Series D convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					14,612,360
Convertible preferred stock, shares issued					13,307,287
Convertible preferred stock aggregate liquidation value | $					$ 79,844,000
Convertible preferred stock, shares outstanding					13,307,287
Dividend rate (in dollars per share) | $ / shares			0.60
Liquidation preference (in dollars per share) | $ / shares			6.00
Series E-1 convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					15,149,375
Convertible preferred stock, shares issued					14,633,509
Convertible preferred stock aggregate liquidation value | $					$ 117,068,000
Convertible preferred stock, shares outstanding					14,633,509
Threshold price of shares issued for exclusion from antidilution protection (in dollars per share) | $ / shares			8.00
Dividend rate (in dollars per share) | $ / shares			0.80
Liquidation preference (in dollars per share) | $ / shares			8.00
Series E-2 convertible preferred stock
Preferred stock
Convertible preferred stock, shares authorized					10,663,125
Convertible preferred stock, shares issued					10,259,189
Convertible preferred stock aggregate liquidation value | $					$ 123,110,000
Convertible preferred stock, shares outstanding					10,259,189
Threshold price of shares issued for exclusion from antidilution protection (in dollars per share) | $ / shares			8.00
Dividend rate (in dollars per share) | $ / shares			1.20
Liquidation preference (in dollars per share) | $ / shares			$ 12.00
Common Stock
Common stock
Reverse stock split ratio		1.0
Issuance of common stock - IPO				10,350,000
Common stock, shares authorized	25,904,241
Common stock, shares outstanding, beginning balance (in shares)			4,286,164	4,286,164	4,161,178	3,827,267
Issuance of common stock - preferred stock conversion to common stock				25,904,241
Common stock, shares outstanding, ending balance (in shares)				41,110,127	4,286,164	4,161,178
Preferred stock
Preferred stock, par value | $ / shares	$ 0.00001