Equity Incentive Plans - Number and Weighted Average Grant-Date Fair Value of Unvested Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding Beginning Balance, Number of Options	998,170	1,350,590	796,514
Granted options during the period, Number	310,000	455,000	1,319,500
Vested options during the period, Number	(819,818)	(651,530)	(654,022)
Forfeited options during the period, Number	(31,905)	(7,106)	(74,335)
Exercised options during the period, Number	(904)	(148,784)	(37,067)
Outstanding Ending Balance, Number of Options	455,543	998,170	1,350,590
Unvested options at the beginning of the period, Weighted Average Grant-Date Fair Value	$ 3.69	$ 2.79	$ 2.60
Granted options during the period, Weighted Average Grant-Date Fair Value	$ 4.10	$ 4.30	$ 2.70
Vested options during the period, Weighted Average Grant-Date Fair Value	$ 3.61	$ 2.68	$ 2.32
Forfeited options during the period, Weighted Average Grant-Date Fair Value	$ 3.20	$ 3.92	$ 4.02
Exercised options during the period, Weighted Average Grant-Date Fair Value	$ 3.16	$ 2.46	$ 1.87
Unvested options at the end of the period, Weighted Average Grant-Date Fair Value	$ 4.18	$ 3.69	$ 2.79