Preferred Stock, Common Stock and Stockholders' Equity - Summary of Nonvested Options Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value Per Share, Granted	$ 1.87	$ 2.04
2007 Plan and 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Options Nonvested, Outstanding beginning balance	690,961
Options, Granted	856,000
Options Vested	(526,607)
Options Nonvested, Outstanding ending balance	1,020,354	690,961
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value Per Share, Nonvested beginning balance	$ 3.34
Weighted Average Grant Date Fair Value Per Share, Granted	2.45
Weighted Average Grant Date Fair Value Per Share, Vested	3.22
Weighted Average Grant Date Fair Value Per Share, Nonvested ending balance	$ 2.65	$ 3.34