Income Taxes - Summary of Provision for Income Taxes (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
United States federal tax statutory rate, Amount	$ (12,801)	$ (9,642)
State taxes (net of deferred benefit), Amount	(786)	(662)
Non-deductible expenses, Amount	253	1,556
Research & Development Credits, Amount	(1,532)
Change in unrecognized tax benefits, Amount	606
Change in valuation allowance, Amount	13,868	20,733
Adjustment for valuation allowance recorded as part of purchase accounting, Amount	0	(11,785)
Other, net, Amount	392	(200)
Provision for income taxes, Amount	$ 0	$ 0
United States federal tax statutory rate, Percent of Pretax Earnings	34.00%	34.00%
State taxes (net of deferred benefit), Percent of Pretax Earnings	2.00%	2.30%
Non-deductible expenses, Percent of Pretax Earnings	(0.70%)	(5.50%)
Research & Development Credits, Percent of Pretax Earnings	4.10%	0.00%
Change in unrecognized tax benefits, Percent of Pretax Earnings	(1.60%)	0.00%
Change in valuation allowance, Percent of Pretax Earnings	(36.80%)	(73.10%)
Adjustment for valuation allowance recorded as part of purchase accounting, Percent of Pretax Earnings	0.00%	41.60%
Other, net, Percent of Pretax Earnings	(1.00%)	0.70%
Provision for income taxes, Percent of Pretax Earnings	0.00%	0.00%