Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Stockholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized shares	90,000,000	90,000,000
Common stock, issued shares	68,757,354	68,227,171
Common stock, outstanding shares	68,757,354	68,227,171
Series A
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Series B
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	750,000	750,000
Preferred stock, outstanding shares	750,000	750,000
Preferred stock liquidation preference	$ 930,000	$ 922,500
Series C
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	177,904	177,904
Preferred stock, outstanding shares	177,904	177,904
Preferred stock liquidation preference	$ 97,847	$ 97,847
Series D
Stockholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	1,751,005	1,751,005
Preferred stock, outstanding shares	1,751,005	1,751,005
Preferred stock liquidation preference	$ 5,002,470	$ 4,961,324