Preferred Stock - Additional Information (Detail) - USD ($)					12 Months Ended
	Jul. 21, 2015	Jun. 11, 2015	Apr. 17, 2014	Jan. 10, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 20, 2013
Temporary Equity [Line Items]
Preferred stock, shares authorized	10,000,000				10,000,000
Preferred stock, par value	$ 0.001				$ 0.001
Preferred stock, shares outstanding					0	0
Shares issued, price per share	$ 17.00
Conversion of convertible securities, shares issued, value					$ 2,543,000
Number of shares issued upon exercise of stock warrants	390,680				481,671
Number of convertible preferred stock issued upon exercise of stock warrants					390,032
Share price		$ 5.215
Preferred stock, voting rights description					Each share of Preferred Stock had a number of votes equal to the number of shares of common stock into which it was convertible. The holders of the Series B and C redeemable convertible preferred stock each had the right to elect one director to the Board. The holders of the Series D redeemable convertible preferred stock had the right to elect two directors to Board. The holders of the common stock and Preferred Stock, voting together on an as-converted basis, elect the three remaining directors.
Preferred stock, dividend percent					8.00%
Cumulative unpaid dividends in arrears						$ 14,400,000
Percentage of accrued but unpaid dividends paid in shares		50.00%
Percentage of accrued but unpaid dividends forfeited		50.00%
Cumulative unpaid dividends in arrears	$ 18,900,000
Convertible preferred stock, redemption amount						5,400,000
Qualified IPO [Member] | If closing occurs on or before April 17, 2015 [Member]
Temporary Equity [Line Items]
Percentage of common stock price over original issue price					160.00%
Share price					$ 8.344
Qualified IPO [Member] | If closing occurs after April 17, 2015 [Member]
Temporary Equity [Line Items]
Percentage of common stock price over original issue price					200.00%
Share price					$ 10.43
Qualified IPO [Member] | Minimum [Member]
Temporary Equity [Line Items]
Proceeds from initial public offering					$ 50,000,000
Series C Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issued, shares				344,664
Shares issued, price per share				$ 5.215
Issuance of stock and warrants, shares				261,737
Proceed from issuance of stock				$ 1,400,000
Conversion of convertible securities, shares issued				82,927
Conversion of convertible securities, shares issued, value				$ 400,000
Number of shares issued upon exercise of stock warrants	93,017				37,385
Number of convertible preferred stock issued upon exercise of stock warrants					93,017
Convertible preferred stock, original issue price					$ 5.215
Cumulative unpaid dividends in arrears	$ 1,700,000					$ 1,100,000
Issuable common stock to redeemable convertible preferred stockholders					161,536
Fair value of common stock to redeemable convertible preferred stockholders					$ 4,400,000
Liquidation Price Per Share						$ 5.642
Percentage of redemption price over liquidation preference						150.00%	150.00%
Series D Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issued, shares			11,409,360
Shares issued, price per share			$ 5.215
Proceed from issuance of stock			$ 56,200,000
Redeemable convertible preferred stock, issuance cost			$ 3,300,000
Convertible preferred stock, original issue price					$ 5.215
Cumulative unpaid dividends in arrears						$ 3,400,000
Cumulative unpaid dividends in arrears	$ 6,100,000
Issuable common stock to redeemable convertible preferred stockholders					589,410
Fair value of common stock to redeemable convertible preferred stockholders					$ 16,000,000
Liquidation Price Per Share						$ 5.510
Percentage of redemption price over liquidation preference						150.00%	150.00%
Series B-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Number of shares issued upon exercise of stock warrants	291,164				444,286
Number of convertible preferred stock issued upon exercise of stock warrants					291,165
Convertible preferred stock, original issue price					$ 2.6075
Cumulative unpaid dividends in arrears	$ 1,700,000					$ 1,500,000
Accruing dividends					$ 800,000
Liquidation Price Per Share						$ 3.656
Percentage of redemption price over liquidation preference					150.00%	150.00%	150.00%
Series B Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Number of shares issued upon exercise of stock warrants	6,499
Number of convertible preferred stock issued upon exercise of stock warrants					5,850
Convertible preferred stock, original issue price					$ 7.45		$ 7.45
Cumulative unpaid dividends in arrears	$ 9,400,000					$ 8,400,000
Accruing dividends					$ 4,700,000
Liquidation Price Per Share						$ 12.268
Percentage of redemption price over liquidation preference					150.00%
Series B Redeemable Convertible Preferred Stock [Member] | Minimum [Member]
Temporary Equity [Line Items]
Convertible preferred stock, conversion price					$ 6.705
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock converted into common stock shares	252,817
Convertible preferred stock, original issue price					11.324
Preferred stock, dividend rate per share					0.79268
Liquidation Price Per Share						$ 11.324
Series A Convertible Preferred Stock [Member] | Minimum [Member]
Temporary Equity [Line Items]
Convertible preferred stock, conversion price					$ 10.0575
Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Conversion of convertible securities, shares issued						82,927	1,495,276
Preferred stock converted into common stock shares	18,109,136				(17,913,767)
Share price				$ 5.215				$ 5.125
Redeemable Convertible Preferred Stock [Member] | Qualified IPO [Member]
Temporary Equity [Line Items]
Preferred stock, redemption terms					In the event of a qualified IPO, the holders were entitled to 50% of the then accrued but unpaid accruing dividends in cash and the remaining 50% were forfeited.
Payment of dividends						$ 7,200,000
Series B and B-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Accruing dividends					$ 5,500,000
Series C and D Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Issuable common stock to redeemable convertible preferred stockholders					750,946
Fair value of common stock to redeemable convertible preferred stockholders					$ 20,400,000