Stock-Based Compensation - Narrative (Detail) (USD $)	12 Months Ended										12 Months Ended					12 Months Ended		1 Months Ended			12 Months Ended	1 Months Ended				12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Consultants [Member]	Dec. 31, 2013 Stock Options [Member]	Dec. 31, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2013 Restricted Stock Units (RSUs) [Member] Consultants [Member]	Dec. 31, 2013 2006 Plan [Member]	Dec. 31, 2012 2006 Plan [Member]	Dec. 31, 2006 2006 Plan [Member]	Dec. 31, 2013 2006 Plan [Member] Monthly Vesting Period [Member]	Dec. 31, 2013 2006 Plan [Member] Stock Options [Member]	Dec. 31, 2013 2006 Plan [Member] Stock Options [Member] Annual Vesting Period [Member]	Dec. 31, 2013 2010 Plan [Member]	Nov. 29, 2010 2010 Plan [Member]	Dec. 31, 2013 2010 Plan [Member] Monthly Vesting Period [Member]	Dec. 31, 2013 2010 Plan [Member] Annual Vesting Period [Member]	Jun. 30, 2012 Restated 2010 Plan [Member]	Dec. 31, 2013 Restated 2010 Plan [Member]	Dec. 31, 2012 Restated 2010 Plan [Member]	Dec. 31, 2013 Inducement Plan [Member]	Nov. 30, 2013 Purchase Plan [Member] Employee Stock [Member]	May 31, 2013 Purchase Plan [Member] Employee Stock [Member]	Nov. 30, 2012 Purchase Plan [Member] Employee Stock [Member]	May 31, 2012 Purchase Plan [Member] Employee Stock [Member]	Dec. 31, 2013 Purchase Plan [Member] Employee Stock [Member] Purchase_Period	Dec. 31, 2012 Purchase Plan [Member] Employee Stock [Member]	Dec. 31, 2013 Purchase Plan [Member] Employee Stock [Member] Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved										1,134,000					2,243,668			9,300,000			2,700,000					409,646	463,973
Expected term								10 years						10 years
Vesting term												4 years		4 years
Vesting rights percentage											2.08333%		25.00%			2.08333%	25.00%
Percent of additional shares authorized provision																		4.00%
Maximum amount deductible																					$ 1,000,000
Shares available for future issuance																			456,854	701,976	1,728,000
Shares outstanding						1,331,000
Weighted average remaining contractual term						4 months 24 days
Aggregate intrinsic value						4,577,000
Unvested shares expected to vest						1,301,000
Common stock price (in usd per share)	$ 3.44
Percentage of purchase price																										85.00%
Maximum percentage of employee withholding																										20.00%
Maximum number of shares per employee																										20,000
Offering period																										6 months		27 months
Number of purchase periods																										2
Exercised (in shares)																						99,024	205,303	138,826	225,053
Weighted average fair value of options outstanding (in usd per share)	$ 2.46	$ 2.64
Total unrecognized compensation costs					12,647,000
Recognition over weighted average periods				3 years 3 months 18 days	2 years 8 months 24 days		4 months 24 days
Unvested stock options outstanding (in shares)				182,000
Unvested restricted stock outstanding (in shares)							25,000	0	0
Unrecognized compensation expense				574,000
Stock-based compensation	$ 8,006,000	$ 6,157,000	$ 4,809,000	$ 323,000