Stock-Based Compensation - Narrative (Detail)		1 Months Ended		12 Months Ended
	Dec. 03, 2013 USD ($)	Mar. 31, 2017 $ / shares shares	Jun. 30, 2012 shares	Dec. 31, 2017 USD ($) offering_period purchase_period $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 04, 2013 shares	Dec. 31, 2010 shares	Dec. 31, 2006 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised | $				$ 14,300,000	$ 24,000	$ 300,000
Stock-based compensation | $				6,155,000	$ 7,353,000	$ 6,941,000
Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation | $				(700,000)
Total unrecognized compensation costs | $				$ 9,200,000
Recognition over weighted average periods				2 years 4 months 1 day
Shares subject to outstanding restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock units granted (in shares)		159,000		175,000
Weighted-average grant date fair value per share, granted (in usd per share) | $ / shares		$ 10.20		$ 10.42
Stock-based compensation | $				$ 0
Restricted stock units vested (in shares)				0	0	0
Weighted average remaining contractual term				2 months 12 days
Intrinsic value of restricted stock units, nonvested | $				$ 3,900,000
2006 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved									141,750
Expected term					10 years
2006 Plan [Member] | Shares subject to outstanding common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term					4 years
2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved								280,459
Expected term				10 years
Vesting term				4 years
Restated 2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved			1,162,500	756,524	571,778
Percent of additional shares authorized provision			4.00%
Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved				102,276	236,625		337,500
Maximum amount deductible | $	$ 1,000,000
Employee Stock Purchase Plan [Member] | Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved				16,672	21,356
Duration of each offering period under the ESPP				12 months
Number of purchase periods permitted under the ESPP | purchase_period				2
Duration of each purchase period under the ESPP				6 months
Number of offering periods permitted under the ESPP | offering_period				2
Percentage of purchase price				85.00%
Maximum percentage of employee withholding				20.00%
Maximum number of shares per employee				2,500
Number of shares purchased during period (shares)				35,934	35,164	25,204