Stockholders' Equity - Summary of Stock Option Transactions (Detail) - Stock Options [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares Available for Grant
Beginning balance (in shares)	6,149	606,061
Additional shares authorized (in shares)	560,717	270,764
Options granted (in shares)	(538,500)	(955,713)
Options canceled/forfeited (in shares)	99,700	85,037
Ending balance (in shares)	128,066	6,149	606,061
Number of Options Outstanding
Beginning balance (in shares)	1,858,839	1,072,011
Options granted (in shares)	538,500	955,713
Options exercised (in shares)	0	(83,848)
Options canceled/forfeited (in shares)	(99,700)	(85,037)
Ending balance (in shares)	2,297,639	1,858,839	1,072,011
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 4.82	$ 6.34
Options granted (in dollars per share)	1.59	3.08
Options exercised (in dollars per share)	0.00	3.50
Options canceled/forfeited (in dollars per share)	2.33	5.03
Ending balance (in dollars per share)	$ 4.09	$ 4.82	$ 6.34
Weighted average remaining contractual term (in years)	8 years 9 months 7 days	8 years 9 months	8 years 8 months 1 day