Stockholders' Equity - Additional information (Detail) - USD ($)			1 Months Ended	12 Months Ended
	Dec. 16, 2015	Jul. 02, 2015	Jul. 11, 2011	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2012	Feb. 28, 2017	Mar. 31, 2016	Dec. 31, 2014	Dec. 03, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company employees, directors and affiliates stock option exercised				202,519	147,425	235,480
Proceeds from common stock				$ 439,000	$ 297,000	$ 755,000
Preferred Stock, par value				$ 0.001	$ 0.001
Authorized shares of preferred stock				5,000,000	5,000,000
Number of RSUs vested				363,701
Common stock authorized beginning balance				75,000,000	75,000,000
Weighted average grant date fair value of options granted				$ 1.46	$ 1.75	$ 4.99
Number of options granted in period with exercise price below market price				0	0	0
Unrecognized compensation cost related to non-vested share-based compensation awards granted				$ 5,500,000
Unrecognized compensation cost related to non-vested share-based compensation awards granted year				3 years
Options outstanding				2,712,954	3,468,991	3,397,529				3,196,100
Fair value of warrants				$ 6,000,000
2011 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares of common stock authorized				7,100,000
2011 Equity Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized beginning balance				11,050,000
2011 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized beginning balance				18,150,000
Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock options outstanding and exercisable			890,693
Term that options may be awarded			10 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity instruments awarded in period				2,357,315
Fair market value of RSUs granted				$ 4,700,000
Vesting period of options				3 years
Restricted Stock Units (RSUs) [Member] | LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity instruments awarded in period				0	0	35,000
Restricted stock units ("RSUs") issued to directors and key employees				1,078,000			978,000
Restricted stock units reserved for future officers						100,000
RSU's Vested per performance criteria during period				8 years
Number of RSUs vested				9,958	13,347	21,356
Series A Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized shares of preferred stock				2,290,700
Series A Preferred shares issued				2,093,155							2,709,300
Liquidation, dissolution or winding up, holders of the Series A Preferred per share payment											$ 0.001
Series A Preferred stock converted				0	0	45,845
Employees and Directors Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company employees, directors and affiliates stock option exercised				200,000	100,000	200,000
Proceeds from common stock				$ 400,000	$ 300,000	$ 800,000
Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding				84,986
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's securities for shelf registration		$ 150,000,000
Universal shelf registration amount, maximum		$ 40,000,000
Company employees, directors and affiliates stock option exercised				202,519	147,426	223,923
MidCap Financial Trust [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock					84,986
Exercise price of warrants					$ 3.53
Fair value of warrants					$ 50,000
CRG [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock				349,451				1,701,583
Exercise price of warrants				$ 3.42				$ 2.38
Fair value of warrants				$ 1,500,000				$ 4,500,000
CRG [Member] | Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding				2,051,034
Dr. Andrew Finn [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period shares upon employee retirement	513,221
Issuance of common stock upon employee retirement									150,000
Employee retirement date				Dec. 31, 2015
Directors and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity instruments awarded in period				956,675
Fair market value of shares granted				$ 1,400,000
Term of options granted period				10 years
Directors and Employees [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU's Vested per performance criteria during period				1 year
Directors and Employees [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSU's Vested per performance criteria during period				3 years